Where Our Water Comes From

With ever-present cycles of drought and few local water resources to depend on, PWP works hard to manage its water resources and maintain a reliable, safe drinking water supply for its customers. Most of our water is imported from the Colorado River and Northern California, but a substantial portion of our water is acquired from our local aquifer, the Raymond Basin.

Local Water from The Raymond Basin

The Raymond Basin, a 40 square mile natural aquifer underlying Pasadena and neighboring cities, provides approximately 40 percent of Pasadena’s drinking water supply. The basin water originates as rain falling in the San Gabriel Mountains. As the water percolates deep into the ground over many months it is cleansed through natural filtration processes. PWP has 7 wells that tap into the basin at depths of 300-500 feet, drawing out 13 million gallons of groundwater or more per day, on average.

Imported Water from the Metropolitan Water District of Southern California (MWD)

The Raymond Basin cannot provide enough water to meet demand, even in wet years, as our population and development has long outpaced local supply. PWP has purchased imported water from the Metropolitan Water District of Southern California (MWD) since 1941. MWD uses aqueducts to transport water from the Colorado River and from the Sacramento-San Joaquin River Delta to 26 member agencies, including PWP, in arid Southern California.

MWD's two sources of water are the State Water Project and the Colorado River. The State Water Project is owned by the State of California and operated by the State Department of Water Resources. The State Water Project transports water available from the Sacramento-San Joaquin Delta to Southern California via the California Aqueduct. Management of the availability of State Water Project supplies through water marketing and groundwater banking plays an important role in meeting California's water needs.

To obtain its Colorado River supply, MWD has a permanent service contract with the United States Secretary of the Interior for delivery of water via the Colorado River Aqueduct. Under the priority system that governs the distribution of Colorado River water made available to California, MWD holds the fourth priority right.

How Water is Delivered to Your Home

PWP’s water system begins with “production,” which in our case means pumping local groundwater and the purchased imported water. There are active wells across the city that tap into the Raymond Basin, a natural aquifer underlying Pasadena and neighboring cities. PWP pumps the groundwater at these well sites, treats it to eliminate microbes or other contaminants, and then either diverts it to a reservoir for short-term storage or pumps it directly into underground water mains for distribution to  our customers. Pumps near reservoirs and booster stations also build pressure in the system to aid in moving water through the system.

Resource Improvements and Long Term Projects

PWP is also investing in alternatives methods for boosting local supply, such as recycled water and stormwater capture. The Water System and Resources Plan of 2020 is our long-term strategic plan for a sustainable water supply and for meeting environmental mandates.

PWP is enhancing the water supply reliability by developing the Non-Potable Water Project. The project will offset up to 10% of the total water consumed by PWP customers by delivering non-potable water sources for public landscape irrigation use in the future.

The Monk Hill basin is an aquifer that runs below Hahamongna Watershed Park in the Arroyo Seco. It serves as a vital local groundwater resource with the Monk Hill Treatment Plant treating water pumped from three nearby wells: Arroyo Well, Well 52 and Ventura Well.

The Monk Hill Water Facility began service on July 6, 2011. Located in Northwest Pasadena near JPL, the facility is part of an ongoing effort to remove perchlorate and volatile organic compounds (VOCs) from the groundwater near NASA-operated JPL, which was the site of Army rocket testing decades ago. The plant is funded by NASA by the Federal government.

PWP Water System Facts:

  • Service area of 26 square miles in Pasadena, Altadena and San Gabriel
  • 14 reservoirs with total storage capacity of 110 million gallons
  • 19 booster stations
  • 1 groundwater treatment facility