It acts as an endocrine disruptor and can impact hormone regulation in both humans and aquatic life, especially with chronic exposure.

Acanthamoeba primarily affects the eyes, causing redness, blurred vision, pain, and sensitivity to light—particularly dangerous for contact lens wearers. In rare cases, it can cause skin infections or a life-threatening condition called granulomatous amoebic encephalitis in immunocompromised individuals.

Prolonged exposure may cause skin and respiratory irritation. PAHs are also linked to environmental and health risks with chronic exposure.

Can contribute to skin, eye, or respiratory irritation and may settle into pool sediments.

It's non-toxic, but its presence indicates human waste contamination and may signal broader water quality issues.

Exposure can cause eye irritation, coughing, and increased respiratory sensitivity.

Generally non-toxic in trace pool concentrations but indicates pharmaceutical contamination.

It can cause skin and eye irritation, corrode metal components in pool systems, and degrade pool surfaces over time. Low pH also makes chlorine more aggressive, leading to excessive sanitizer consumption.

Itself not harmful, but can form biofilms that protect harmful bacteria or protozoa.

These bacteria can support the growth of more harmful microbes if biofilms develop, especially in warm or untreated pools.

May cause skin or eye irritation at high levels. Known to be moderately toxic to aquatic organisms.

Can cause respiratory infections, skin or wound infections—especially in people with weakened immune systems.

May cause skin, wound, or respiratory infections, particularly in immunocompromised individuals.

Acrolein exposure causes eye irritation, skin redness, throat discomfort, coughing, and breathing difficulties. Prolonged exposure can lead to lung inflammation and increased respiratory sensitivity.

Not dangerous, but can contribute to cloudy water and promote algae buildup.

Adenovirus infections cause red, irritated eyes, sore throat, fever, cough, stomach cramps, and diarrhea. It is especially concerning in young children, the elderly, and individuals with weakened immune systems.

Aeromonas can cause skin rashes, ear infections, diarrhea, vomiting, and eye irritation. In severe cases, it may lead to wound infections or bloodstream infections in immunocompromised individuals.

Aflatoxins are linked to liver toxicity, immune suppression, and cancer with long-term exposure. While the risk of direct poisoning from pool water is low, inhalation or contact with contaminated surfaces can contribute to health concerns.

Long-term exposure may cause hormone disruption and increase cancer risk.

Usually harmless, but in rare cases can cause minor infections or indicate poor sanitation.

Algae make pool surfaces slimy and unsafe, clog filters, and can create a breeding ground for bacteria. Severe algae blooms can also stain pool surfaces and make swimming unappealing.

Exposure can cause rashes, eye irritation, nausea, vomiting, respiratory issues, and in rare cases, liver or neurological damage. Children and pets are especially vulnerable due to smaller body weight and likelihood of swallowing water.

Low alkalinity causes pH fluctuations, corrosion of pool surfaces, and eye/skin irritation while high alkalinity leads to cloudy water, scaling on pool surfaces, and makes it harder to adjust pH.

Even at low levels, alkylphenols can interfere with hormone function, affect aquatic life, and contribute to foaming, scum lines, and poor water clarity in pools.

Linked to hormone disruption, neurotoxicity, and cancer in long-term exposure.

Can trigger asthma, allergies, or skin irritation in sensitive individuals.

Excess alum residue may cause cloudy water, clog filters, lower pH, and contribute to aluminum buildup, which can irritate skin and eyes or cause staining.

High aluminum levels can turn water cloudy, cause skin and eye irritation, and lead to white or grayish stains on pool surfaces. When aluminum reacts with chlorine, it may form insoluble compounds that settle on the pool floor, creating unwanted deposits. Excess aluminum may also interfere with water balance and sanitizer effectiveness.

A suspected endocrine disruptor that may cause mild skin or eye irritation with prolonged exposure.

Ammonia leads to high chloramine levels, causing eye and skin irritation, strong odors, and reduced chlorine effectiveness. It also increases chlorine demand, making maintenance more costly.

High ammonium levels cause eye and skin irritation, respiratory discomfort, and reduced chlorine efficiency, leading to increased chemical demand and poor sanitation.

Some amoebas, like Naegleria fowleri, can cause severe and often fatal brain infections (PAM) if water enters the nasal passage. While rare, the consequences are extremely serious.

While generally low in toxicity, amyl acetate can irritate the eyes, throat, and lungs—especially in indoor pools with poor ventilation. It may also affect sensitive swimmers or contribute to unwanted odors.

Anatoxin-a disrupts nerve communication, leading to symptoms such as muscle twitching, dizziness, difficulty breathing, and in extreme cases, paralysis or death. Pets are especially at risk if they drink contaminated water.

Animal feces can carry parasitic eggs, like raccoon roundworm, which can lead to diarrhea, fever, organ damage, and in the case of raccoon roundworm, severe neurological infections. It may also introduce E. coli, Giardia, or Cryptosporidium, causing gastrointestinal distress.

Exposure can irritate skin and eyes and may pose long-term health risks. These agents are toxic to algae and can disrupt pool ecology and filtration systems.

Excess antimony may cause skin and eye irritation, stomach discomfort, or respiratory problems when inhaled as airborne particles near heated indoor pools. Long-term exposure is linked to liver and heart issues.

Long-term arsenic exposure can cause skin irritation, respiratory issues, and serious health conditions. Even in low concentrations, it's a hazardous contaminant that should be removed immediately.

Asbestos is a known carcinogen. Inhalation is the main concern, but ingestion through contaminated water may also contribute to health risks. It does not dissolve and remains suspended in water.

Ash can clog filters, stain pool surfaces, and unbalance water chemistry. It may introduce heavy metals and organics that cause skin irritation, cloudy water, and reduced sanitizer effectiveness.

Asphalt and tar residue can create stubborn black stains on pool liners, tiles, and skimmers. It forms an oily, floating residue that makes the water appear dirty and can clog filters, reducing their effectiveness. The residue may react with pool chemicals, leading to foaming or cloudy water, and make pool surfaces slippery, creating a safety hazard.

Atrazine exposure has been linked to skin irritation, hormonal disruptions, and environmental concerns. While not immediately dangerous in low levels, it's best to prevent buildup.

Atrazine and its metabolites are suspected endocrine disruptors and may interfere with hormone regulation. They're also toxic to aquatic organisms and can contribute to chemical instability in pools.

Harmful bacteria can cause skin infections, ear infections, gastrointestinal issues, and even serious diseases like E. coli and Legionella.

High barium levels can cause staining and water quality issues. Ingestion through contaminated water may lead to gastrointestinal problems and more severe health concerns.

Bather load contaminants reduce chlorine effectiveness, form chloramines, cause irritation, and increase chlorine demand. Oils can clog filters and cause cloudy water.

Exposure to benzene can cause headaches, dizziness, nausea, respiratory issues, and long-term toxicity including increased cancer risk.

Though not acutely toxic, benzotriazole can disrupt aquatic ecosystems and may pose long-term risks to human health due to its persistence and bioaccumulative potential. It may interfere with UV disinfection and alter pool chemistry.

Beryllium is a known respiratory toxin and potential carcinogen. While skin contact with beryllium-contaminated water poses low risk, inhaling particles (especially in indoor pools with poor ventilation) can cause chronic beryllium disease (CBD), a serious lung condition.

Exposure can lead to respiratory irritation, asthma exacerbation, allergic reactions, or in rare cases, infections such as Legionnaires' disease. Risk increases in poorly ventilated or overcrowded environments.

Surfactants cause foam, reduce water clarity, and may clog filters. While biodegradable, they don't break down instantly and can still create water chemistry issues.

Biofilm reduces chlorine effectiveness, leads to persistent water issues, and can cause infections.

Bird droppings carry harmful pathogens like E. coli, Salmonella, and Giardia, causing illness. They also increase chlorine demand and cause staining.

While generally low in toxicity, bismuth buildup can discolor water, interfere with sanitizer performance, and form insoluble compounds that cloud the pool or stain surfaces.

Excess body oils make the water look dirty, clog filters, and reduce sanitizer effectiveness, leading to increased chemical use.

Low levels stabilize pH and improve clarity, but high levels cause irritation and can harm pets or children if ingested.

Inhalation or skin contact with bromoform can cause irritation, dizziness, or nausea. Long-term exposure may contribute to organ damage or cancer risk.

Cause strong odors, skin/eye irritation, respiratory discomfort, and reduce sanitizer effectiveness.

Long-term exposure to bromates is linked to health concerns, including an increased risk of cancer. While not an immediate threat in low levels, bromates should be minimized.

Exposure to BDBPs can cause eye and skin irritation, respiratory issues, and long-term health risks like increased cancer potential. Inhalation of these byproducts, especially in poorly ventilated areas, may worsen asthma and lung irritation.

Long-term exposure to BFRs has been linked to hormonal imbalances, developmental toxicity, and potential neurological effects.

Bromine effectively kills bacteria and algae, but it can cause skin irritation in some people and has a strong chemical smell when it forms bromamines. It also has a longer residual effect than chlorine, which may lead to stronger odors and buildup.

Calcium scale builds up on pool walls, plumbing, and equipment. It reduces water clarity, damages heaters, clogs pipes, and can irritate swimmers' skin and eyes.

Even low levels of cadmium exposure can cause skin irritation, eye discomfort, and respiratory issues. Long-term exposure is linked to kidney damage, weakened bones, and cancer risk. Unlike some metals, cadmium does not easily dissolve, meaning it can settle in pool sediments or accumulate in filtration systems.

Calcium scale clogs filters, damages heaters, clouds water, and creates rough surfaces that irritate skin. It also reduces the efficiency of sanitizers.

Low Calcium: Causes etching and damage to plaster, grout, and pool surfaces. High Calcium: Leads to scale buildup on equipment, cloudy water, and rough pool surfaces.

Balanced carbonate levels help buffer pH changes, preventing fluctuations that can make pool maintenance difficult. However, excess carbonates cause high total alkalinity (above 120 ppm), which leads to scaling, cloudy water, and reduced chlorine effectiveness. If carbonate levels are too low, pH swings become more frequent, increasing corrosion risks to metal components and pool surfaces.

These compounds can cause foaming, skin irritation, cloudy water, and decreased sanitizer efficiency. Some also form sticky residues that trap debris.

These nanoparticles may contribute to water cloudiness, interfere with filter function, and are still being studied for potential long-term health effects. They may also alter chlorine activity in unexpected ways.

While low levels of chloral hydrate in pools do not pose an immediate risk, prolonged exposure can lead to eye irritation, respiratory discomfort, and potential nervous system effects.

Chloramines cause eye and skin irritation, respiratory discomfort, and reduce chlorine’s effectiveness. They also contribute to poor air quality in indoor pools, leading to a condition known as “lifeguard lung.”

Proper chlorine levels keep water safe and clean, but too much chlorine can cause eye/skin irritation, while too little allows bacteria and algae to grow.

High levels of chlorine dioxide can cause eye irritation, skin sensitivity, and respiratory discomfort. It can also react with pool chemicals to create chlorinated byproducts, which may lead to poor water quality, strong chemical odors, and reduced sanitizer efficiency.

Inhalation of chlorine gas can cause burning eyes, throat irritation, coughing, breathing difficulty, and in extreme cases, chemical burns in the lungs.

At low levels, chlorite and chlorate do not significantly impact swimmers, but high concentrations can cause irritation to the skin, eyes, and respiratory system. Excess chlorate may also reduce chlorine efficiency, leading to poor sanitation and increased chlorine demand. Long-term exposure to high levels of chlorate in drinking water has been linked to potential thyroid and blood-related health effects, making it important to monitor and minimize buildup in pool water.

Long-term exposure to high levels of chloroform may increase health risks, including potential carcinogenic effects and respiratory issues. Short-term exposure can cause dizziness or irritation.

Exposure may cause respiratory irritation, headaches, nausea, and long-term health concerns including potential carcinogenic effects. These compounds can also worsen indoor air quality.

Chlorophenols are responsible for strong, medicinal or musty odors in pool water, sometimes mistaken for excessive chlorine. They reduce chlorine efficiency, leading to increased chlorine demand and poor sanitation. High concentrations can cause skin and eye irritation and contribute to disinfection byproduct (DBP) formation, which can impact water and air quality, especially in indoor pools.

High chromium levels can cause skin irritation, respiratory discomfort, and an increased risk of long-term health issues. It can also leave greenish stains on pool surfaces.

Cloudy water reduces visibility, which is a safety hazard, and often indicates poor sanitation. It can also signal ineffective filtration or imbalanced chemistry, both of which can lead to equipment damage or increased chemical use.

High levels of cobalt can cause blue, gray, or purple stains on pool surfaces, particularly on plaster or fiberglass finishes. Prolonged exposure may cause skin irritation or allergic reactions in sensitive individuals. Additionally, cobalt contamination can affect water clarity and interfere with pool chemical balance.

Coliform bacteria can cause gastrointestinal illness, infections, and other health risks if ingested or introduced through open wounds. High coliform levels indicate poor sanitation and potential exposure to harmful pathogens like E. coli.

Discolored water can signal contamination and is often a warning sign of chemical imbalance or filtration problems. It may stain pool surfaces, damage equipment, and reduce swimmer confidence in water cleanliness.

Excess copper can cause blue-green staining on pool walls, ladders, and fixtures, and in some cases, swimmer's hair can turn green after prolonged exposure. Copper buildup may also lead to skin irritation and water discoloration.

Corrosive water can deteriorate ladders, pumps, heaters, and even pool liners. It may cause metal stains on pool surfaces, eye/skin irritation, and increased repair costs.

Exposure to cresols can cause skin irritation, eye burning, respiratory issues, and in high concentrations, potential toxicity.

Crypto causes cryptosporidiosis, a severe diarrheal illness that can last up to two weeks, along with symptoms like vomiting, dehydration, stomach cramps, and fever. It is especially dangerous for children, the elderly, and individuals with weakened immune systems. Unlike many pathogens, Crypto has a thick outer shell that makes it resistant to chlorine, requiring special treatment to eliminate it.

Even in small amounts, cyanide exposure can lead to respiratory issues, dizziness, nausea, and headaches. At high concentrations, cyanide is extremely toxic and can interfere with oxygen use in the body, posing life-threatening risks. While rare in well-maintained pools, poor water source quality, chemical runoff, or accidental contamination can introduce cyanide into pool water.

Although no longer "alive," DNA fragments may still carry harmful genetic material or residual toxins. They can clog filters, reduce clarity, and trigger allergic reactions or irritation in sensitive individuals.

Exposure can cause skin rashes, eye irritation, nausea, liver damage, and respiratory issues. Some cyanotoxins are linked to neurological disorders with long-term exposure.

Even at low levels, cyanogen chloride is a severe eye, skin, and respiratory irritant. Swimmers may experience burning eyes, coughing, shortness of breath, and chest discomfort. In high concentrations, cyanogen chloride is classified as a chemical warfare agent, making it a significant concern for air quality in indoor pools.

Proper CYA levels help maintain chlorine effectiveness, but too much CYA reduces chlorine's ability to sanitize the pool.

Cyclospora infections cause severe diarrhea, dehydration, stomach cramps, and nausea.

Exposure can cause skin rashes, eye irritation, nausea, liver damage, and long-term toxicity risks.

While harmless in small quantities, residual DE can cloud pool water, irritate eyes and lungs when airborne, and contribute to filter clogging or pump wear if not contained.

Decomposition releases phosphates and nitrogen into the water, promoting algae growth and cloudy water. It can also reduce chlorine effectiveness and cause foul odors, stains, and clogged filters.

Detergents and soaps create excessive foaming on the water's surface and make pool water feel slimy or filmy. They can also cause eye and skin irritation, clog filters with residue, and reduce chlorine effectiveness, making it harder to maintain proper sanitation. High concentrations may lead to cloudy water and increased chlorine demand.

Diatom buildup clogs pool filters, makes surfaces slippery, and contributes to algae-like growth in pools.

DBAA is considered a possible human carcinogen. DBAA may cause eye, skin, and respiratory irritation. Long-term exposure has been linked to liver and reproductive system damage in laboratory studies.

Dibromochloromethane is linked to respiratory irritation, eye discomfort, and potential long-term health risks such as liver and kidney damage.

DCAA is linked to liver toxicity, skin and eye irritation, and potential long-term health risks when consumed or absorbed in high amounts. It also reduces water quality by increasing chlorine demand and contributing to chemical odors.

Though marketed as safer, DINCH may still pose low-level health risks with prolonged exposure. In pools, it contributes to chemical buildup, may irritate sensitive skin, and can alter water chemistry over time.

Dioxins are known to cause serious health risks, including skin irritation, immune system suppression, hormone disruption, and potential carcinogenic effects with long-term exposure. Even in small amounts, dioxins can accumulate in the body over time, making it essential to limit exposure in pool water.

Debris clogs filters, stains pool surfaces, and provides nutrients for algae growth. It also increases chlorine demand, making it harder to keep the water clean.

DBPs can cause respiratory issues, eye and skin irritation, and strong chlorine odors. In poorly ventilated areas, high DBP levels can impact air quality. Long-term exposure to some DBPs is linked to potential health risks.

High TDS levels can lead to dull, cloudy water, scaling, and reduced chlorine effectiveness, leading to more frequent maintenance and chemical adjustments. Water can also taste salty or feel less refreshing.

Ingestion or exposure to domoic acid can cause dizziness, confusion, nausea, memory loss, and in severe cases, neurological damage.

Contact with the larvae can cause intense itching, red bumps, and skin irritation that resemble mosquito bites. Though not dangerous, it's uncomfortable and may take days to resolve.

These chemicals can mimic or block hormones, potentially leading to developmental, reproductive, neurological, and immune issues. Effects may build up with prolonged exposure.

Linked to hormonal imbalances, thyroid dysfunction, fertility problems, and other long-term health effects.

Can trigger inflammation, rashes, congestion, coughing, and flu-like symptoms; worse in indoor pools.

Cause fever, vomiting, diarrhea, sore throat, and in rare cases, severe conditions like meningitis.

Epoxides may cause skin and eye irritation, disrupt water clarity, and react with chlorine to form unwanted byproducts. Some are suspected to be carcinogenic with long-term exposure.

Can cause diarrhea, vomiting, stomach cramps, and infections, especially in children or immunocompromised individuals.

May disrupt hormone balance and endocrine function; long-term exposure poses ecological and health risks.

Ethanolamines can reduce sanitizer efficiency, cause foaming, skin irritation, and cloudiness in water. They also contribute to nitrogen levels, increasing the risk of chloramine and DBP formation.

Causes chemical odor, irritation, headaches, and long-term damage to organs with prolonged exposure.

Can cause redness, itchiness, and irritation around the eyes, especially in those with weakened immune systems.

Can lead to outbreaks of illnesses like E. coli, Giardia, and Cryptosporidium, causing severe diarrhea, infections, and spread of waterborne illnesses.

Cause skin rashes, eye irritation, respiratory issues, and filtration problems if not removed.

Disrupt hormones, may impair development and thyroid function, and are difficult to remove once present.

Excess fluoride can cause water chemistry imbalance and potential irritation.

Foam can be unsightly and reduce water clarity. It can trap bacteria, interfere with sanitation, and leave behind sticky or oily residues. In severe cases, foaming may indicate poor water quality or chemical imbalance.

Irritates eyes, throat, and skin; long-term exposure may raise cancer risk.

Fragrance chemicals can irritate eyes and skin, contribute to foaming, and react with chlorine to form volatile organic compounds (VOCs). Sensitive individuals may experience allergic reactions.

Causes skin and eye irritation, clogs filters, stains surfaces, and reduces chlorine effectiveness.

Exposure can cause athlete's foot, skin irritation, and allergic reactions in sensitive individuals.

Causes slimy surfaces, musty odors, water discoloration, skin rashes, respiratory issues, and biofilm buildup.

Causes diarrhea, dehydration, cramps, and nausea; spreads easily in unsanitized pools.

Glycol ethers can irritate skin, eyes, and lungs. In water, they may react with disinfectants and increase chlorine demand.

Alters pool chemistry, increases chlorine demand, and can cause skin irritation or dizziness.

Turns water green, clogs filters, creates slippery and unsafe surfaces.

Long-term exposure to alpha radiation through drinking or bathing water can increase the risk of cancer and organ damage. While alpha particles don't penetrate skin, they are hazardous when ingested or inhaled.

HAAs have been linked to skin and eye irritation, liver toxicity, and long-term cancer risks with prolonged exposure.

Some HANs are toxic, potentially damaging DNA and contributing to long-term health risks. Short-term exposure may cause irritation to the eyes, skin, and respiratory system. Prolonged or repeated exposure may increase risk of reproductive or developmental issues.

Many halogenated hydrocarbons are carcinogenic and can cause liver, kidney, and nervous system damage. Short-term exposure may lead to skin irritation, eye discomfort, and respiratory issues.

High calcium levels cause scale buildup on pool surfaces and equipment, reducing efficiency and increasing maintenance costs.

High metal levels can cause staining on pool surfaces, green or brown water, and hair discoloration in swimmers.

Hepatitis A causes fever, nausea, jaundice, and liver inflammation. It can spread easily in public pools if proper sanitation isn't maintained.

These acids can cause brown or tea-colored water, stain surfaces, increase chlorine demand, and react with disinfectants to form harmful DBPs like THMs.

Humic substances give water a yellow or brown tint, making it look dirty. They also react with chlorine to form DBPs like trihalomethanes (THMs), which have potential health risks.

Exposure can cause skin burns, respiratory irritation, nausea, and long-term cancer risks.

It causes eye, skin, and respiratory irritation, neurological effects, and stains surfaces.

Hydroquinone can cause skin irritation, eye redness, and long-term exposure risks, including depigmentation and potential organ damage. It may react with chlorine to form harmful byproducts.

I-DBPs have been associated with cytotoxic and genotoxic effects. Exposure may lead to respiratory irritation, eye discomfort, or potential cellular damage with repeated contact.

IPBC may cause skin or eye irritation, especially in warm spa environments where absorption is increased. It can also interact with chlorine and form disinfection byproducts. It may also interfere with sanitizer effectiveness in hot tubs.

Irgarol can harm beneficial microorganisms in the pool ecosystem, contribute to chemical instability, and irritate sensitive skin. It's particularly problematic in natural swimming pools or systems with biological filtration.

It causes murky water, stains, and potential plumbing damage.

Excess leads to 'chlorine lock', reducing chlorine effectiveness.

In water, isopropanol evaporates quickly but contributes to VOC levels and increases chlorine demand. It may cause minor skin and eye irritation in sensitive users. In enclosed spaces, it can worsen air quality or pose fire risks if misused.

Can cause skin infections, 'hot tub rash', eye irritation, and respiratory issues.

Ketone exposure can cause dizziness, headaches, skin irritation, and respiratory discomfort. Prolonged exposure may lead to central nervous system effects and organ toxicity.

Exposure to Klebsiella can lead to pneumonia, urinary tract infections, and skin rashes, especially in those with weakened immune systems.

Swimmers with latex allergies may experience skin irritation, redness, or breathing difficulties. Rubber particles can clog filters, reduce clarity, and cause scum lines.

Lead exposure is linked to neurological damage, developmental delays in children, kidney issues, and cardiovascular problems. It can also irritate skin and eyes.

Inhalation of Legionella-contaminated mist can cause flu-like symptoms, fever, cough, shortness of breath, and potentially life-threatening pneumonia.

Inhalation of contaminated water mist can cause Legionnaires' disease, leading to flu-like symptoms, fever, cough, shortness of breath, severe respiratory infections, and potentially life-threatening pneumonia.

Symptoms include fever, chills, muscle aches, vomiting, jaundice, and in severe cases, organ failure.

Lignin can turn water brown, stain pool surfaces, and reduce chlorine effectiveness. It can also contribute to biofilm formation if not properly managed.

Lipopeptides contribute to slippery surfaces, cloudy water, and sanitizer-resistant bacterial colonies. This promotes biofilm growth, leading to cloudy water, unpleasant odors, and persistent contamination.

Residues clog filters, reduce chlorine effectiveness, and lead to cloudy or greasy water. Some chemical additives in sunscreens may also react with chlorine, forming unwanted byproducts.

High manganese levels can turn water brown or purple, stain pool surfaces, and react with chlorine, leading to additional chemical imbalances.

Manganese dioxide can stain pool surfaces, clog filters, and cause brown or black discoloration. Fine particles may also reduce water clarity or be mistaken for algae.

Mercury exposure can damage the brain, nervous system, and kidneys. It can also impair development in children and affect the immune system. Long-term exposure is particularly dangerous. It is bioaccumulative and difficult to detect without specific testing.

Methane buildup in water can cause bubbling or foaming, and in poorly ventilated indoor pools, it can reduce oxygen levels and pose a suffocation risk.

MSA may lower pH unexpectedly and contribute to corrosive water. It can also interact with other disinfection byproducts and may be irritating to the eyes or skin at elevated levels.

Exposure to MTBE can cause respiratory irritation, headaches, dizziness, and nausea. Long-term exposure is linked to liver and kidney damage.

Exposure can cause dizziness, headaches, respiratory irritation, and in high doses, neurological damage. It may also pose a long-term cancer risk.

MIT can cause skin irritation, allergic contact dermatitis, and eye discomfort. Sensitized individuals may experience rashes even at low concentrations.

Biofilms reduce chlorine effectiveness, allowing harmful bacteria to thrive and cause skin rashes, ear infections, and respiratory issues.

MVOCs cause strong odors, skin irritation, respiratory discomfort, and allergic reactions.

Microcystins can cause skin irritation, eye inflammation, nausea, vomiting, diarrhea, and liver damage. Inhaling mist from contaminated water may lead to respiratory irritation or asthma-like symptoms. Long-term exposure is linked to neurological disorders and organ toxicity.

They can trigger allergies or respiratory irritation and contribute to slippery surfaces or cloudy water. In immunocompromised individuals, they may trigger infections or worsen allergies. In rare cases, they may grow into visible fungal colonies on grout or pool walls.

Microplastics are difficult to remove, may reduce water clarity, and can harbor bacteria or chemical pollutants. They can irritate skin, accumulate in pool filters, and contribute to long-term environmental concerns.

While low levels of molybdenum are generally harmless, excessive exposure can cause metallic stains on pool surfaces, water discoloration, and potential toxicity with prolonged ingestion.

Mustard algae creates a slimy layer on pool surfaces making them slippery, clogs filters, and can return even after treatment if not fully eradicated. It can also harbor bacteria, increasing chlorine demand and making pool water unsafe.

Inhalation of aerosolized MAC may lead to pulmonary infections. It can also cause skin infections or lymph node swelling, especially in children and immunocompromised individuals.

Exposure can cause skin rashes, respiratory distress, and potential immune system effects.

Linked to respiratory irritation, reproductive toxicity, and potential carcinogenicity. Volatile forms can be inhaled in indoor pools, while others remain dissolved in water.

Even in small doses, NDMA may damage the liver and is linked to cancer in animal studies. It's volatile and can also be inhaled, increasing exposure risk.

In rare cases, Naegleria fowleri can cause a fatal brain infection known as primary amebic meningoencephalitis (PAM). Infection is extremely rare but nearly always fatal.

While research on nanoparticles in pool water is still developing, certain types may alter water chemistry, disrupt filtration, and contribute to skin or respiratory irritation. Some nanoparticles, such as silver or titanium dioxide from sunscreens, can react with chlorine, forming unwanted byproducts. Their small size makes them hard to remove using traditional filtration methods.

While research is ongoing, nanoplastics may cause cellular damage, disrupt hormone systems, and accumulate in tissues. They also contribute to cloudy water and filter clogging.

Exposure to naphthalene can cause eye and skin irritation, headaches, dizziness, and respiratory discomfort. Long-term exposure is linked to liver and kidney toxicity, anemia, and potential cancer risks.

Though not typically harmful to humans, their presence signals poor sanitation. In rare cases, parasitic varieties can cause skin or gastrointestinal irritation. They can reduce water clarity and contribute to biofilm development.

High nickel levels can cause green, gray, or black staining on pool surfaces and equipment. Swimmers with nickel allergies may experience skin irritation, rashes, or contact dermatitis. Over time, nickel can accumulate in filters and pipes, leading to plumbing corrosion and reduced water quality.

High nickel levels can cause greenish or black stains on pool surfaces and swimmer hair discoloration. In some cases, skin irritation or allergic reactions may occur, particularly in those sensitive to nickel.

High nitrate levels make algae growth almost unavoidable, leading to increased chlorine demand and poor water quality, making pool maintenance more difficult and expensive.

Long-term exposure to nitrosamines has been linked to potential cancer risks.

NPEs mimic hormones and may cause reproductive and developmental effects. In water, they foam, interfere with chlorine, and degrade slowly—making them long-term pollutants.

Can act as an endocrine disruptor, affecting hormone function, and cause water foaming or cloudiness.

Bad pool smells are more than a nuisance—they can cause eye irritation, respiratory discomfort, and indicate that the water isn't properly sanitized. Prolonged exposure in indoor pools can affect air quality and health.

Oil buildup creates scum lines, cloudy water, clogs filters, and reduces chlorine effectiveness.

Oily films can clog filters, trap debris, reduce chlorine effectiveness, and cause slippery or stained surfaces. They may also contribute to unpleasant smells or cloudy water.

Causes severe gastrointestinal illness, including diarrhea, dehydration, and stomach cramps.

Organic matter consumes chlorine, promotes algae growth, and creates unpleasant smells and cloudy water. It can contribute to the formation of chloramines, causing eye and skin irritation.

Organochlorine pesticides are linked to hormone disruption, liver toxicity, neurological issues, and an increased cancer risk. Even at low levels, long-term exposure can lead to health concerns.

Organotins can damage the immune system, disrupt hormones, and are toxic to aquatic organisms. They may also irritate skin or eyes upon direct contact.

They can cause eye irritation, skin dryness, cloudy water, and foul odors. Some are volatile and accumulate in indoor air, while others persist in water and reduce sanitizer effectiveness.

Oxidized organic compounds reduce chlorine efficiency, contribute to poor water clarity, and create irritating chemical odors. Some byproducts, like chloramines and trihalomethanes (THMs), can cause eye irritation, skin sensitivity, and respiratory discomfort, especially in indoor pools with poor ventilation.

Ozone improves water clarity, reduces chloramine formation, lowers chemical demand, and effectively kills bacteria and viruses. However, excessive ozone exposure can cause respiratory irritation, especially in poorly ventilated areas. It also does not provide lasting disinfection in pool water, meaning chlorine or bromine is still required for continuous sanitation.

Paint particles can cloud water, clog filters, and irritate eyes or skin. Some older coatings may contain harmful substances like lead or VOCs.

Parabens and preservatives can reduce chlorine efficiency, create scum lines, and make pool water cloudy. Some parabens may also mimic hormones, leading to concerns about their long-term effects on human health and aquatic environments. Prolonged exposure can cause skin irritation, allergic reactions, and increased chemical demand in pool maintenance.

Parasitic worms can cause intestinal infections, skin rashes, and allergic reactions. Some types, such as hookworms and schistosomes, can penetrate the skin, leading to conditions like swimmer’s itch or more severe parasitic infections. Ingestion of contaminated water can result in stomach cramps, diarrhea, and long-term health complications.

PCBs are known carcinogens and hormone disruptors. Prolonged exposure, even in low concentrations, has been linked to immune system damage, neurological issues, skin rashes, and liver toxicity. Because PCBs do not dissolve easily in water, they can attach to pool surfaces, accumulate in filters, and form chemical films on the water's surface.

PCP is a potential carcinogen and can affect liver, kidney, and respiratory function. Even small amounts can cause skin and eye irritation or allergic reactions.

High levels of peracetic acid can cause eye and skin irritation, respiratory discomfort, and a strong chemical odor. Prolonged exposure may lead to corrosive damage to pool liners, metal fixtures, and filtration equipment.

Perchlorates can interfere with thyroid function, leading to potential health concerns over long-term exposure. In pool water, they reduce chlorine efficiency, making it harder to maintain proper sanitation. High perchlorate levels may also cause chemical imbalances, leading to cloudy water and increased chemical demand.

PFC exposure is linked to hormonal disruption, immune system suppression, liver damage, and an increased risk of certain cancers. Even at low levels, PFCs accumulate in the body over time, leading to potential long-term health effects. In pool water, PFCs can alter water chemistry and be difficult to remove with standard filtration methods.

Exposure to pesticides and herbicides can cause skin irritation, eye discomfort, and potential long-term health risks. Some chemicals may also react with chlorine, altering pool water chemistry, reducing sanitation effectiveness and forming unwanted byproducts.

PFAS exposure has been linked to hormonal imbalances, immune suppression, liver and kidney damage, thyroid dysfunction, and an increased risk of cancer. These chemicals can bioaccumulate in the body, meaning even low-level exposure over time can have serious health effects. In pool water, PFAS do not easily break down, potentially leading to long-term contamination.

Low pH (acidic) can cause eye irritation, skin discomfort, and corrosion of metal fixtures. High pH (alkaline) can lead to cloudy water, scale buildup, and reduced chlorine effectiveness.

While most are present in low concentrations, PPCPs can interfere with endocrine systems, cause allergic reactions, or promote antimicrobial resistance with long-term exposure.

Phenols reduce chlorine efficiency, cause eye and skin irritation, and create chemical odors. Long-term exposure to chlorophenols may have toxic effects on the liver and kidneys.

Though generally safe, PHMB can cause eye and skin irritation if used incorrectly. It is incompatible with chlorine and certain algaecides, potentially causing cloudy water or residue.

High phosphate levels create algae problems, making pool maintenance more difficult and increasing the need for chemical treatments.

Long-term exposure to phthalates has been linked to hormonal imbalances, fertility issues, developmental disorders, and potential cancer risks. In pool environments, they can cause water contamination and residue buildup on surfaces.

Pink slim can cause skin irritation, eye infections, and increase chlorine demand by forming a resistant biofilm. It can also clog filters and cause slippery surfaces, making pool maintenance more difficult.

Although marketed as safer, non-phthalate plasticizers may still have health and environmental concerns. They can cause oily films, cloudy water, and skin irritation. Some may also act as endocrine disruptors over long-term exposure.

Pollen can turn water yellow or green, reduce water clarity, and increase chlorine demand as it decomposes. Spores may contribute to mold, algae growth, and biofilm formation in poorly maintained pools. Swimmers with allergies or respiratory issues may experience irritation when pollen levels are high.

PCT exposure is linked to liver and kidney damage, immune suppression, and potential cancer risks. These compounds also accumulate in the body over time.

PAHs are known to be harmful to human health, with long-term exposure linked to cancer, organ damage, and skin irritation. In pool water, they can cause oily films, scum buildup, and discoloration, making the water unappealing and harder to maintain. PAHs also increase chlorine demand, making sanitation less effective.

Povidone-iodine can discolor water, stain surfaces, and react with chlorine to form iodinated disinfection byproducts (I-DBPs), some of which are toxic. It may also disrupt water chemistry and irritate sensitive skin.

Propylene glycol may increase chemical demand, cloud water, and reduce sanitizer effectiveness. While not typically harmful in small doses, buildup can interfere with filtration and contribute to organic loading. In large doses, it may cause skin sensitivity or system imbalance.

Exposure to Pseudomonas aeruginosa can cause red, itchy skin rashes (hot tub folliculitis), eye irritations, ear infections, and in severe cases, respiratory infections, particularly in hot tubs.

Pseudomonas fluorescens contributes to cloudy water, slimy surfaces, increased chlorine demand, and bacterial skin infections. It can also clog filters and harbor more dangerous bacteria.

Pyrethroid exposure can cause skin irritation, dizziness, nausea, and respiratory issues. Some pyrethroids are suspected to be endocrine disruptors.

While effective at controlling algae, excessive quat buildup can cause foaming in pool water and may lead to skin and eye irritation. Some quats can also bind to filters, reducing their effectiveness.

These silicones can cause slick or cloudy water, create buildup on pool surfaces, and reduce chlorine efficiency. Over time, they may clog filters and lead to staining or foaming. They also decrease sanitizer efficiency and may contribute to biofilm development.

Long-term exposure to radioactive contaminants increases the risk of cancer, lung disease, and organ damage. Radon gas, when inhaled, is a leading cause of lung cancer. Uranium and radium in water can affect kidney function and bone health over time. High radiation levels may also degrade pool surfaces and equipment.

Exposure to radioactive isotopes can increase the risk of cancer, radiation poisoning, and organ damage.

Chronic exposure to radium is linked to bone cancer and other serious health issues due to its accumulation in the bones. Though it doesn't penetrate the skin, it can be dangerous if ingested or inhaled through water vapor or dust.

Rainwater lowers pH, dilutes chlorine levels, and introduces organic matter like dirt, debris, and pollutants that fuel algae growth. It also increases the risk of contaminants such as nitrates and phosphates, which can disrupt water balance, reduce sanitizer effectiveness, and cause cloudy or unbalanced water.

Resins can cloud water, stick to filters, and cause irritation. Some resins may release volatile compounds or leach chemicals if damaged or exposed to UV. Prolonged exposure may lead to fiberglass fiber release.

Rodent contamination can introduce Leptospirosis, Salmonella, E. coli, and Hantavirus, leading to severe gastrointestinal, respiratory, and skin infections. Even indirect exposure, such as swimming in contaminated water, can cause eye and ear infections, fever, and rashes. Rodent feces may also increase organic waste, affecting water clarity and sanitation.

Swallowing contaminated water can cause stomach cramps, dehydration, vomiting, and diarrhea. The virus is highly resistant to chlorine at normal levels.

Rotifers aren't harmful to humans, but their eggs can accumulate and reduce water clarity, clog filters, and signal broader contamination from other microorganisms or organic matter. Their presence often points to inadequate water treatment or environmental exposure.

Rubber particles cloud water, clog skimmers, and contribute to surface grime. Some may also leach chemicals that interfere with water balance or sanitizer performance.