Before the establishment of Monterey One Water (then Monterey Regional Water Pollution Control Agency, MRWPCA), every community in the Monterey Bay area had its own sewage treatment plant.  Most of the communities were discharging into the Monterey Bay — in some cases as little as 300 feet off shore. The Federal Clean Water Act of 1972 effectively stopped that practice and increased treatment standards.

In November 1972, M1W was formed by Monterey, Pacific Grove, and Seaside Sanitation Districts. Over the years, many other northern Monterey County entities eventually became Joint Powers Authority (JPA) participants in the regional system as well (as detailed below).

In addition to Federal Clean Water Act requirements, it became evident during the early 1970s that the quality of northern Monterey County's groundwater supply was deteriorating because of extensive withdrawal of groundwater for agriculture. This overdraft led to an increasing problem of seawater intrusion, which was threatening the multibillion dollar agricultural industry and the drinking water supply for the City of Salinas.

In the mid-1970s, a group of community leaders began discussing the idea of recycling wastewater. The objective was to retard the advance of seawater intrusion by supplying irrigation water to farmland in the northern Salinas Valley. This would significantly reduce the draw of water from the underground aquifers.

This led to an extensive 11-year Monterey Wastewater Reclamation for Agriculture Study (PDF; 13MB) which began in 1976. The final results of this research proved that recycled water is safe for the irrigation of food crops that are consumed without cooking.  Today, this definitive report is used as the standard in countries all over the world.

Reeside Pump Station in MontereyBy 1983, several phased construction projects were completed utilizing the old coastal treatment plants as pumping stations, connected to one of 3 interceptor pipelines, and a 60-inch diameter outfall pipeline extending 2 miles into the Monterey Bay. Visit the Wastewater Conveyance page for additional information.

Offering economies of scale and concentration of expertise, M1W proposed to operate one regional plant by replacing eight older (and some overloaded) wastewater facilities in Northern Monterey County. 

By the late 1980s all the coastal municipalities and agencies with sewage treatment responsibility were participants in M1W. The participants created a Joint Powers Authority (JPA) with eleven members: representatives from the Monterey County Board of Supervisors, City of Salinas, Boronda County Sanitation District, Castroville Community Services District, City of Del Rey Oaks, City of Monterey, City of Pacific Grove, City of Sand City, City of Seaside, Marina Coast Water District, Moss Landing County Sanitation District, and the U.S. Army as an ex-officio member. Each entity appoints a member to the Board of Directors, who is usually an elected official of that community and serves on the M1W Board solely at the pleasure of the appointing member entity.

Each member municipality is responsible for maintaining and operating its own collection system.  As a courtesy, M1W collects fees on behalf of the entities.  For a listing of entity fees, visit the Residential Rates page.

M1W currently serves a population of approximately 250,000 people and treats 18.5 million gallons each day.

The Regional Treatment Plant (RTP) was constructed two miles north of the City of Marina, near the farmland experiencing the worst seawater intrusion. In February 1990, the RTP began operation with a design capacity to treat up to 29.6 Million Gallons per Day (MGD).  The old treatment plants were then decommissioned. The pumping stations remained to pump sewage (rather than treated wastewater) to the new treatment plant.  Visit the Wastewater Conveyance page for more information.

Facility construction was funded by federal and state grants. The Regional Treatment Plant represents an investment of approximately $150 million: $48 million for the connecting interceptors and pump stations; $28 million for the 60-inch diameter outfall line; and $74 million for the Regional Treatment Plant. Regional Treatment Plant operation and maintenance costs are funded by property owners through bi-monthly billings. Learn how M1W rates are set.

Administrative Offices

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5 Harris Court, Bldg D
Monterey, CA 93940

(831) 372-3367
or (831) 422-1001

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