The Upper San Gabriel Valley Municipal Water District (Upper District) was formed by voters in the San Gabriel Valley on December 8, 1959, to help solve water problems in the rapidly-developing San Gabriel Valley. The District was then incorporated on January 7, 1960. On March 12, 1963, residents of the District voted to annex to the Metropolitan Water District of Southern California (MWD), through whose facilities supplemental water, first from the Colorado River, and now from the State Water Project, is brought into the Valley.
The District played a vital role in determining water rights within the Main San Gabriel Basin by acting as plaintiff in the 1973 court case of Upper San Gabriel Valley Municipal Water District, Plaintiff, v. The city of Alhambra, et al, Defendants. This case brought about the creation of the Main San Gabriel Basin Watermaster which was ordered by the court to administer and enforce provisions of the judgment.
Since 1973, the District initiated a water-quality monitoring program involving chemical and physical constituents in the local domestic water supplies. The appearance of volatile organic compounds (VOCs) in many water wells in the District was first discovered in local water supply wells in 1979. Since approximately 80 percent of the annual water consumption in the San Gabriel Basin is supplied by groundwater, water purveyors have either removed those contaminated wells from service, blended contaminated water with water from other sources, or installed treatment systems to meet health standards and to protect public users.