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Henry J. Mills Treatment Plant

The Henry J. Mills Treatment Plant in Riverside is one of five water treatment plants in the Metropolitan Water District system.

Located off Interstate 215 in the city of Riverside, Mills sits near the Box Springs foothills at an elevation of 1,650 feet, the highest of the five plants.  Mills supplies treated water, via gravity flow, throughout most of the service areas for Eastern Municipal Water District and Western Municipal Water District of Riverside County.

From Mountain High…

The water filtered through this plant originates in northern California's mountains, rivers and streams, and flows through the Sacramento-San Joaquin Delta before entering the State Water Project's 444-mile California Aqueduct.  In emergencies, water from the Colorado River that flows through Metropolitan's 242-mile Colorado River Aqueduct can also be treated at Mills.. Since its dedication in May 1978, Mills has been upgraded from 150 million gallons per day to 220 million gallons per day. At capacity, the plant will clean enough water to fill the Rose Bowl every nine hours.  Automated systems regulate water levels and pressures.  These precise monitoring and surveillance capabilities allow plant operators to anticipate and meet demands, and to respond rapidly to emergency situations.

…To Your Kitchen Faucet

Looking at the plant's web of pipes, pumps and sophisticated electronic gadgetry, filtration appears to be a complicated process. Conventional filtration, however, is surprisingly simple and effective.

Items used are similar to those found in any home, garden or garage.  Upstream grates and screens catch large debris and plants.  At the filtration plant, coal and sand used as filter media remove any particles left in the water. Then, ozone and/or chlorine and ammonia are used as disinfectants.

Conventional filtration involves what is known as coagulation, where aluminum sulfate and other chemical additives cling to particle matter in the water.  These compounds adhere to each other, forming larger particles called floc. Once the water and floc enter large sedimentation basins, the floc settles to the bottom.

From the basins, water filters through the coal and sand layers, and then is disinfected to kill the few remaining microorganisms.  MWD water meets or surpasses all state and federal water quality standards. Mills has been using ozone as its primary water disinfectant since 2003.

Wildlife Protection

An endangered species, the Stephen's kangaroo rat inhabits land outside the perimeter of the Mills plant.  If you look closely; you can spot a knee-high "K-rat" wall that encourages the nocturnal rodent to live and nest within protected areas.

Ensuring the safety of the kangaroo rat is just one example of how Metropolitan continues to mitigate environmental impacts in order to protect threatened and endangered wildlife ecosystems.

Mills The Man

On March 1, 1967, Henry J. "Hank" Mills became the general manager of the Metropolitan Water District.  By the time he retired some four-and-a- half years later, he was wrapping up a 41-year career with Metropolitan.  As general manager, Mills was popular with district employees because he was one of their own--an aqueduct builder who walked the same ground as they did.  His Metropolitan career began on a survey crew, plotting routes for the Colorado River Aqueduct.  From there, he worked his way up the ranks to assistant chief engineer, chief engineer, and finally, general manager, leaving Metropolitan a legacy difficult to match.

Today, many among the more than 1,800 Metropolitan employees work full time  to maintain and upgrade what has become one of the world's largest water distribution systems.

Photo of Mills Treatment Plant
Henry J. Mills Treatment Plant
550 E. Alessandro Blvd.
Riverside, CA 92508
Photo of Mills Treatment Plant

Page updated: October 23, 2013