Water Quality Update

Safe, clean drinking water is a necessity of life, and the Contra Costa Water District works hard to ensure that you and your family have a reliable supply of this necessity.

Overall, tap water in the United States is widely known to be among the safest in the world. Despite that, you have probably read about contaminants in drinking water and want more information. Here is a briefing on the contaminants that have been in the news lately and the status of CCWD water.


In Contra Costa Water District treated water, arsenic has been undetected based on a minimum detection level of 2 parts per billion (ppb) set by the State of California. This is also true of treated water in the cities of Martinez, Pittsburg, Antioch, and Oakley.

The maximum amount of arsenic allowed in water by the State is 50 ppb. CCWD has no problems meeting this standard in its treated water, as arsenic has been undetected.

In CCWD's raw water, data from the past 10 years shows the vast majority of samples tested were below the detection level. In a few isolated raw water samples, arsenic was found between 4 and 7 ppb, well below the maximum allowable level.

Arsenic occurs naturally in the environment, being the 20th most common element in the Earth's crust. It is added to the environment by the weathering of rocks, burning of fossil fuels, smelting of ores and manufacturing. Arsenic concentrations are usually highest in groundwater. CCWD uses surface water, which usually has very low concentrations.

Methy Tertiary Butyl Ether (MTBE)
MTBE is a gasoline additive that reduces air pollution. Gasoline producers began using it extensively in 1992 to meet federal clean air requirements. But MTBE's use is now being phased out in California by 2003, and nationally in the next few years, because it has contaminated some groundwater supplies as the result of leaking fuel tanks or fuel spills.

So far, MTBE has been undetectable at CCWD's Delta intakes, based on State of California testing standards that set the minimum level for detection at 5 parts per billion. To protect the water after it is pumped from our intakes, CCWD does not allow gasoline-fueled recreational boats in its reservoirs. In addition, CCWD is one of many water agencies working to actively pursue solutions to MTBE drinking water contamination.

Mycobacterium Avium Complex (MAC)
MAC is a group of pathogens that is very common in the environment. They can be found in soil, dust and water. Individuals with healthy immune systems normally resist these pathogens. For people with compromised immune systems, these pathogens can cause pulmonary and other health problems.

Conventional treatment processes used by CCWD and other providers are aimed at eliminating pathogens. Filtration, a standard water treatment process, is very effective in removing pathogens such as Mycobacterium avium Complex. Other treatment methods used with filtration, such as chloramine and ozone gas disinfection, increase effectiveness. In addition, the quality of water leaving treatment plants and traveling through distribution pipelines to homes and businesses is monitored frequently.

Chromium is a naturally occurring element. There are several species of chromium, one of which is Chromium-6, an inorganic chemical that can be toxic. Chromium-6 has been in the news lately because it has been found in groundwater, mostly in Southern California, due to industrial contamination. It was the focus of the popular movie "Erin Brockovich." Extensive research is now underway to determine the extent of Chromium-6 contamination throughout the state and its health effects.

CCWD tests its water for total chromium, which includes all types of chromium. Testing has shown CCWD source water to have very low total chromium levels, less than the 10 parts per billion limit established by the state for reporting as "detectable." The maximum allowable level is 50 parts per billion.


Cryptosporidium is a single-cell parasite that lives in fecal matter in the intestines of animal and people. This microscopic pathogen can cause a disease called cryptosporidiosis when humans have oral contact with something contaminated. Drinking untreated water or swallowing contaminated water in a lake or swimming pool are 2 common ways people can contract cryptosporidiosis.

The most common symptoms of cryptosporidiosis are diarrhea, abdominal cramps, nausea, low-grade fever, dehydration and weight loss. People with healthy immune symptoms rarely are sick for more than 2 weeks. However, cryptosporidiosis can be fatal to the very young, elderly, frail and immunocompromised people.

Protection of source water supplies, like the measures CCWD takes at the Los Vaqueros Reservoir Watershed, is an important step toward keeping drinking water free of cryptosporidium. Once water reaches the treatment plant, filtration is used to remove cryptosporidium and other pathogens, and the treated water is tested for the presence of any bacteria in general.

Concerns about drug residues in water supplies have recently been covered in the news media. A handful of small studies has detected antibiotics, hormones and other pharmaceuticals at very low levels (the low parts per trillion) in some water supplies, and the federal government has launched a comprehensive nationwide study to determine the significance of these findings.

Drug residues are released into the environment by humans and animals through their waste. These compounds are generally not removed in the treatment process at wastewater treatment facilities and can make their way back into water supplies.

Some scientists are concerned that antibiotic residues in the environment can eventually cause bacteria to resist these drugs. Other scientists believe the levels of pharmaceuticals being found in water are too low to have a significant effect on human health. This is a very new study area and researchers are continuing to collect data.