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 over 40 percent of Pasadena’s drinking water supply. The basin water originates as surface water from the San Gabriel Mountains. As the water percolates deep into the ground over many months it is purified through natural filtration processes. PWP has 16 wells that tap into the basin at depths of 300-400 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 dry Southern California.

MWD’s two primary 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 San Francisco Bay/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 vast 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.

Since Pasadena topography is on a gentle gradient, gravity forces do most of the work to distribute water through the system. 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 Integrated Resources Plan of 2011 [5.6.3] is our long-term strategic plan for a sustainable water supply and for meeting environmental mandates.

The Arroyo Seco Canyon Project (add link) is a $9 million collaborative effort between PWP and Arroyo Seco Foundation is intended to upgrade the Arroyo Seco stream water intake structure to improve our ability to capture more stream water and to recharge the groundwater basin. This effort is currently on-hold due to pending litigation.

PWP has plans to enhance the water supply reliability by developing the Non-Potable Water Project [3.6.1]. The project will offset up to 10% of the total water consumed by PWP customers by delivering recycled water and other untapped non-potable water sources for landscape irrigation and industrial uses 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 four nearby wells: Arroyo Well, Well 52, Ventura Well, and Windsor Well.

The Monk Hill Treatment Plant began service on July 6, 2011. Located in Northwest Pasadena near JPL, the state-of-the-art water treatment plant is part of an ongoing effort to remove perchlorate and volatile organic compounds (VOCs) from the groundwater near NASA-owned JPL, which was the site of Army rocket testing decades ago. The plant is funded by NASA and backed by the U.S. EPA, California Department of Toxic Substances Control and the Los Angeles Regional Water Quality Board.

PWP Water System Facts:

  • Service area of 26 square miles in Pasadena and Altadena
  • FY2016 Water Sales: 42% local groundwater, 58% imported (less than 1%- other sources)
  • 14 reservoirs with total storage capacity of 110 million gallons
  • 17 active wells
  • 19 booster stations
  • 1 treatment plant (Monk Hill Water Treatment Plant)