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Several drinking water systems in the central San Joaquin Valley don’t meet state and federal drinking water standards because they have unsafe levels of toxic chemicals.

Some of the contaminants are naturally occurring in groundwater, but can become concentrated at unsafe levels when the groundwater table drops. Others are the byproduct of fertilizers and pesticides used in farming and dairy operations, or other industrial pollution.

Do you know whether your drinking water is polluted with a contaminant? If you’re unsure, click here to find out if your water system is contaminant and what pollutants are above healthy levels.

This guide provides a summary of known health risks of contaminants, and how you can protect you and your family if your water is known to be polluted.

Tip: The Environmental Protection Agency requires all community water systems to deliver an annual consumer confidence report to customers each year. Call your water provider to get a copy and ask questions about what it says.

Guide to common drinking water contaminants in Central California

The following information was compiled from reviews by the Centers for Disease Control, Environmental Protection Agency and the State Water Resources Control Board.

How to filter nitrate

Babies who drink water with high nitrate can get seriously ill with Blue Baby Syndrome and can die if not treated. It’s also a health risk for pregnant women.

If your water is contaminated, use bottled water for drinking, cooking and for mixing formulas or juice concentrates. Boiling water or using common filtration systems like Brita filters do not remove nitrate.

The only way to remove nitrate from water is with filtration systems that use ion exchange, distillation, or reverse osmosis.

Nitrate is a natural part of groundwater and soil, but elevated levels are caused by fertilizers used for agriculture, dairies and high concentrations of septic tanks for sewage.

Click here for more information about nitrate.

Arsenic in the water

Drinking water with toxic levels of arsenic can cause nausea, vomiting, diarrhea, dehydration and shock. Long-term exposure to high levels of arsenic in drinking water is associated with skin disorders, diabetes, high blood pressure and increased risk of cancer of the liver, bladder, kidney, lungs and skin.

If your water is contaminated with arsenic, use bottled water. Boiling water does not remove arsenic. Arsenic can be removed with water treatment methods such as reverse osmosis, ultra-filtration, distillation, or ion exchange.

Arsenic can occur naturally or from industrial and agricultural pollution. Groundwater can be contaminated by high levels of arsenic if the water table drops too low as a result of over-pumping.

Click here for more information about arsenic.

1,2,3 Trichloropropane (TCP)

People exposed to 1,2,3-TCP for many years have increased risk of getting cancer. Exposure to high levels can cause irritation to eyes, skin, respiratory system, central nervous system, liver and kidneys.

Boiling the water does not remove 1,2,3-TCP. Home filtration systems using activated carbon can remove the pollution from water, though filters must be changed more often than usual.

1,2,3-TCP is a man-made chemical that was used in fumigant pesticides in agriculture fields across the Central Valley until it was banned in the 1990s. It remains in groundwater.

Click here for more information about 1,2,3-TCP.


Drinking water contaminated with uranium can increase your risk of kidney damage.

Uranium can be removed from drinking water and cooking water using a reverse osmosis drinking water system. Bathing and showering with water contaminated with uranium is not a health risk.

Uranium is a common and naturally occurring radioactive substance.

Click here for more information about uranium.

1,2-Dibromo-3-Chloropropane (DBCP)

Drinking water contaminated with DBCP can result in gastrointestinal distress and pulmonary edema. Exposure at high levels can cause male infertility and increase the risk of cancer.

If your water is contaminated with DBCP, consider using bottled drinking water or using a carbon filter. Showering, bathing or washing dishes with DBCP-contaminated water is a health risk because you can still breathe it in and absorb it through your skin. Boiling water does not help, and may release dangerous vapors.

DBCP was used in pesticides, nematicides, and soil fumigants until it was banned in 1977 in California. It remains in the groundwater.

Click here for more information about DBCP.

Ethylene Dibromide (EDB)

Headaches and depression have been linked to short-term exposure to EDB. Long-term exposure can be harmful to the male reproductive system and the central nervous system and can harm fetal growth and development. It can also cause cancer.

Boiling the water will not remove EDB. It can only be effectively removed by filtering the water through a granulated carbon filter.

EDB was used as a fumigant pesticide and as a gasoline additive until it was banned in California in the 1980s.

Click here for more information about EDB.


Infants and pregnant mothers are particularly at risk from water contaminated with perchlorate. It can decrease production of thyroid hormone, which is needed for fetal and child development and for adults’ metabolism and mental function.

Water contaminated with perchlorate can be used for showering, laundry and dishes, but not for drinking. Boiling water does not remove perchlorate. It can be removed with water treatment technologies using ion exchange and reverse osmosis.

Perchlorate is used in the production of rockets and explosives, and is typically associated with military operations and aerospace programs. It is sometimes present in fertilizers and bleach, and can be naturally occurring.

Click here for more information about perchlorate.


Small amounts of manganese are safe and even considered essential to a healthy diet. However, exposure to high levels of manganese is a health risk, especially for children.

It is regulated for aesthetic reasons not health reasons. Lower levels of manganese in water can stain clothes and taste funny.

Still, high levels of manganese can cause neurological damage and affect motor skills, balance and coordination, as well as increased memory loss and anxiety.

Limit exposure to high levels of manganese by using bottled water for drinking and making formula. Boiling the water does not help and may make it worse. It is considered safe to brush your teeth, shower, bathe, and do dishes with water contaminated with manganese.

Manganese is a common naturally-occuring mineral.

Click here for more information about manganese.


Iron is regulated for aesthetic concerns because it can cause discoloration. It is not considered a health risk.

Iron and calcium can build up in pipes and drains, causing problems for plumbing and appliances. It can be removed using a filtration system or water softener system.

Iron is a naturally-occurring element.

Total trihalomethanes (TTHM)

Potential health effects from long-term exposure to TTHM include damage to the liver, kidney or central nervous system, and increases the risk of cancer, particularly bladder cancer. Exposure can also harm fetal growth development.

Exposure can happen through drinking contaminated water or inhaling water vapors during showers, for example. If your water is contaminated with TTHM, you can reduce exposure by using a carbon filter at the tap or by drinking bottled water.

TTHM is a byproduct created during the water treatment process when chlorine (used to disinfect drinking water) reacts with other natural compounds in water.

Click here for more information about TTHM.

Total Haloacetic Acids (HAA)

Long-term exposure to drinking water with high levels of HAA increases the risk of cancer and can damage the liver, kidneys, neurological and reproductive systems. Effects can include drowsiness, metabolism changes and tingling in fingers and toes. Children are at higher risk.

HAAs are mainly a hazard in water used for drinking or cooking. Exposure to the skin or from vapors while showering is not considered a health risk. Activated carbon filters can remove HAAs from drinking water.

HAA are a byproduct of disinfectants used in drinking water, such as chlorine.

Click here for more information about Haloacetic Acids.

This project was made possible with support from the Central Valley Community Foundation and the Local Government Commission through the S.D. Bechtel, Jr. Foundation Community Foundation Water Initiative.

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