Water Treatment

EBMUD has a history of vigilance about water quality. We work to protect our customers water supply every step of the way by guarding the watershed lands surrounding our reservoirs, testing water as it travels many miles through aqueducts and distribution pipelines, and maintaining the best water storage and treatment.

EBMUD's six water treatment plants can filter and process more than 375 million gallons of water daily (MGD). The water treatment plants are Upper San Leandro in Oakland, San Pablo in Kensington, Sobrante in El Sobrante, and plants located in and named for Orinda, Lafayette and Walnut Creek.

The Orinda Water Treatment Plant has the largest output, with a maximum capacity of 200 MGD. This plant serves all or parts of Alameda, Albany, Berkeley, El Cerrito, Emeryville, Moraga, Oakland, Orinda, Piedmont, Richmond and San Leandro. The other plants supply water in varying amounts to the balance of the EBMUD service area.

Every drop of water delivered to customers is filtered through sand, and anthracite or carbon. Each water treatment plant also provides disinfection, fluoridation and corrosion control.


Water Quality Map

Water Quality Map

Water Treatment Steps


Water entering the plant is sprayed into the air through nozzles, producing a fountain-like effect. Breaking the water into small drops creates a proper oxygen balance, releasing trapped gases that can cause objectionable tastes and odors.


EBMUD adds coagulants to the water in mixing basins. The coagulants neutralize particles, allowing them to join together. These particles are removed in subsequent steps.


After coagulants are added, the water is gently mixed to cause particles to combine and grow large enough to settle.


The water flows into sedimentation basins where the particles settle to the bottom. This step removes about 85 percent of the suspended matter in the water. Water for the next step (filtration) is collected from the top of the sedimentation basins.


Any remaining particles are trapped and removed during filtration. The almost clear water from the sedimentation basins flows into deep, concrete-walled boxes. At the bottom are filter beds made up of layers of anthracite and sand. Particles are trapped in these layers as the now-clean water flows down through the filters to a collecting system.


The addition of a chlorine solution kills any pathogenic microscopic life, such as bacteria or viruses. Finely controlled amounts of chlorine are added on an ongoing basis. Prior to leaving the treatment plant, small amounts of ammonia are added to the chlorine to form chloramine, a more stable disinfectant, that will last longer in the distribution system.


At Sobrante and Upper San Leandro water treatment plants, ozone is used for disinfection and control of taste and odor causing compounds.


EBMUD is required by regulation to add a small amount of fluoride to the water to promote dental health.

Corrosion Control

EBMUD adds calcium hydroxide (lime) or sodium hydroxide to the water at the source or at water treatment plants to control corrosion. Using lime to achieve a slightly alkaline chemical balance prevents the water from corroding EBMUD's distribution pipes and consumers' plumbing. This keeps substances like lead from leaching out of plumbing fixtures and into the drinking water.