Water Quality

During warm months when algae blooms are more likely in the Delta, Zone 7 adds powdered activated carbon to the water to remove some of the harmless taste-and-odor-causing compounds, such as geosmin, released by algae.

The Department of Water Resources monitors for toxic compounds released by algae, including cyanotoxins produced by some blue-green algae, throughout the State Water Project. In addition, Zone 7 implemented its own algal toxins monitoring in 2016. Blue-green algae are appearing more frequently in water bodies such as the Delta and Lake Del Valle, which supply water to Zone 7.

A study of Zone 7’s source water identified ozone as the only effective treatment of such cyanotoxins. Zone 7 is designing improvements that will add ozone treatment to surface water provided to DSRSD and other Tri-Valley water retailers. In addition to removing algal toxins, ozonation will reduce disinfection by-products and improve the taste and odor of our water more effectively than current treatments. Provided that Zone 7 obtains construction financing, ozonation is scheduled to begin at the Del Valle treatment plant by 2019 and at the Patterson Pass plant by 2021.

Yes. Nearly all water contains some fluoride, but usually not enough to help prevent tooth decay or cavities. Community water systems can add the right amount of fluoride to their local drinking water to prevent tooth decay. Voters in the District’s service area approved fluoridation in 1974 and treatment began in 1977.

DSRSD maintains the optimal level of 0.7 milligrams of fluoride per liter of water (mg/L) and a control range of 0.6 to 1.2 mg/L, as required by federal and state regulations. In 2015, the U.S. Department of Health and Human Services Agency recommended that water systems adjust their fluoride content to this new optimal level, as opposed to the previous temperature-dependent optimal levels ranging from 0.7 mg/L to 1.2 mg/L. There was no change regarding health officials' strong and long-standing support regarding the value of fluoridation of drinking water. More information on fluoridation is available on the Centers for Disease Control and Prevention and State Water Resources Control Board websites.

Yes. As of July 1, 2014, California’s drinking water standard for chromium 6 allowed up to 10 parts per billion (ppb), and all the water DSRSD purchases from Zone 7 meets this standard. In May 2017, a court decision invalidated the standard, known as a maximum contaminant level (MCL). The court found that regulators had not properly considered the economic feasibility of complying with the MCL. The State Water Board is in the process of re-establishing an MCL for chromium 6. Until it does, chromium 6 is regulated by the 50 ppb MCL for total chromium. Visit the State Water Board’s chromium 6 information page for details.

Zone 7 has stated it will maintain operational procedures to keep chromium 6 below 10 ppb despite the court decision. Typically 80 percent of our drinking water supply consists of treated surface water from the State Water Project. Zone 7’s treatment process removes the chromium 6, if any, in that water. Zone 7 also uses groundwater from five well fields during the summer or when the surface water supply is interrupted. In 2016, the Chain of Lakes Well Field had chromium 6 levels up to 12 parts per billion. Per a state-approved blending plan, Zone 7 blends this well water with water from other sources so all the water flowing to customer taps has less than 10 ppb of chromium 6.

News reports have discussed California’s “public health goal” for chromium 6, which is 0.02 ppb. A public health goal is not a maximum “safe” level for exposure to a chemical. Rather, it estimates the “one in one million” lifetime cancer risk: for every million people who drink tap water with that level of chromium 6 each day for 70 years, there is likely to be one additional case of cancer from exposure to the chemical.

Public health goals are not drinking water standards, and no water agencies are required to meet them. The State Water Board sets the enforceable drinking water standard, the MCL, as close to the public health goal as possible after considering costs, benefits, and the ability of water utilities to detect and remove the contaminant during water treatment.

Hardness is caused by naturally occurring minerals and is measured by the amount of calcium carbonate in the water, expressed either as milligrams per liter (mg/L) or grains per gallon (gpg). Our water is moderately hard to hard, with 90 percent of samples in the range of 115-324 mg/L (7-19 gpg). Because our water is a variable blend of surface and well water, hardness changes throughout the year and by location in the district. During shortages of surface water supplies (such as from the State Water Project), water hardness can be higher than normal because Zone 7 is blending in more groundwater. Zone 7 also may minimize operation of its demineralization plant to conserve water.

Samples collected from many places along the distribution pipelines are tested at least once a month for coliform bacteria, chlorine residuals, and fluoride. In addition, fluoride is monitored 24/7 online, and daily field samples are taken to ensure compliance with the operating range required by the state’s Division of Drinking Water (DDW). Field samples are also cross-checked weekly in the DSRSD lab. Other water quality parameters, including pH, hardness, alkalinity, conductivity, turbidity, and color, are monitored monthly. The level of total dissolved solids (TDS) is checked weekly. We monitor for other contaminants according to schedules established by DDW or other regulatory agencies. Zone 7 also performs many quality tests before it delivers the water to DSRSD.

Yes, both DSRSD and Zone 7 test for lead. In addition, Zone 7 adjusts the pH of our water to prevent plumbing corrosion, which is the main source of lead in tap water. Learn more on our Lead page.

Please contact Customer Service at (925) 828-8524 or CustomerService@dsrsd.com.

The District discourages customers from installing self-regenerating water softeners because they add excess amounts of salt to our wastewater, which in turn increases the salinity of recycled water used for irrigation. Learn more on our Water Hardness & Softeners page.

Zone 7 uses a demineralization process to slow down the buildup of salts and minerals in our groundwater basin and reduce the hardness of groundwater pumped from the Mocho Wellfield in western Pleasanton. During water shortages, Zone 7 may minimize demineralization, since some water is lost during the process.

East Bay Municipal Utility District (EBMUD) gets most of its water from the Mokelumne River watershed and channels it into an aqueduct east of the Sacramento-San Joaquin Delta. The water never passes through the delta and that’s why it tastes different than DSRSD’s water, which is a blend of surface water that has flowed through the delta and groundwater extracted from local wells. DSRSD’s water will taste less like the delta once Zone 7 begins ozone treatment (see next question).

Many factors can affect the taste of water. DSRSD’s water is a blend of surface water and groundwater. The blend changes throughout the year and these variations can change taste and odor. Chlorine used to disinfect the water supply occasionally produces a chemical odor. Rapid algae growth in the delta can cause an earthy, musty, or plastic taste or odor. (Algae “blooms” can occur at any time but are most common from late spring through early fall.) These changes in taste or odor do not affect the safety of the water.

Rotting food in garbage disposal or bacteria in the P-trap under the drain can also cause a foul smell. To get rid of the odor, fill the sink with hot water, add an ounce of household bleach, and allow the water to drain slowly. If you have a water filter on your faucet or refrigerator, be sure to change it as often as recommended; otherwise, it becomes a breeding ground for bacteria that can make you sick.