Hidden in a Hill – Perris Hill Reservoir

First built in 1949 to provide water to St. Bernadine Medical Center, the Perris Hill Reservoir serves as drinking water storage for the people in the City of San Bernardino. This hidden reservoir is not visible to the naked eye; it was intentionally constructed inside an existing hill, east of Perris Hill Park. A popular hiking spot for locals, the Perris Hill Reservoir is hidden deep in the earth. From the top of the hill, only the beautiful surrounding mountains of San Bernardino are seen. It is beneath this hilltop location where 10 million gallons of water are stored every day to provide a resource essential to all life; water. In 1962, the Perris Hill Reservoir was reconstructed to expand the capacity in order to meet the demands of the growing region.

Perris Hill Exterior
Perris Hill Reservoir is hidden beneath the soil at Perris Hill.

“In the 1940’s the need for additional water storage was identified. There wasn’t enough water for the hospital and the surrounding area,” stated Michael Garland, Water Utility Operations Superintendent at San Bernardino Municipal Water Department. “Because of its depth, Perris Hill Reservoir is technically classified as a dam by the State of California. There are many benefits to building a dam in a hill. Not only does it provide needed pressure to deliver water, but it also keeps the temperature cooler, versus an outdoor tank.”

The Perris Hill Reservoir, owned and operated by San Bernardino Municipal Water Department (SBMWD), is just one of 38 reservoirs operated by the Department. In 2016, SBMWD served 202,000 people, equating to 10.5 billion gallons of water.  The Perris Hill Reservoir provides water to 3,284 households.

Perris Hill Reservoir 6
Rarely seen view of the interior of Perris Hill Reservoir after being drained.

Every eight years, the reservoir is drained for routine maintenance. The structure is disinfected, inspected and repairs are made. In January 2018, the Perris Hill Reservoir was drained and inspected. When the tank is empty, a large 20-inch pipe is visible on the floor of this damp, cool compound. This pipe is used to keep water moving inside the reservoir in order to minimize stagnation. Water enters the reservoir through the pipe; this is called the influent line. It leaves the pipe via another pipe called the effluent line. The constant movement helps ensure safe clean reliable water delivery to the consumers’ homes.

Perris Hill Reservoir Stairs
When the Perris Hill Reservoir is filled to capacity, water covers the entire staircase.

“Crews prepared for the draining of Perris Hill Reservoir by first determining the water demand of the reservoir. The water is not wasted, we simply shut off production from the well, so that no new water is entering the tank,” explained Garland. “We deplete the water from reservoir by the usage from our customers. Once the water is drained (used) we switch service so that the customers who would normally receive water from Perris Hill Reservoir receive water from another location. The entire process of draining takes approximately 10 days to complete.”

Perris Hill Reservoir does not have any on-site staff members who work at the location, however the monitoring of water levels and quality is logged multiple times a day. Daily water quality samples are collected and analyses are performed to ensure the safety of the drinking water.

Sensors help detect water levels inside the Reservoir.

“Our staff comes out to the site multiple times a day to report water levels and quality. Water levels can also be tracked remotely using a transducer, which uses sonar technology to report water levels,” shared Garland. “All of our facilities, including the Perris Hill Reservoir, record data relating to water supply using a computerized system for tracking real time data called Supervisory Control and Data Acquisition (SCADA).”

Viee Perris Hill Reservoir
View from the top of Perris Hill. The Perris Hill Reservoir sits just below this hilltop.

Water stored in the Perris Hill Reservoir comes from local water supplies, including groundwater basins and snowmelt from the San Bernardino Mountains. The San Bernardino area is a part of the Santa Ana River Watershed, an intricate system of natural water sources starting as snowmelt in the San Bernardino Mountains, traveling down through Riverside, then after multiple uses to Orange County for recharge into the groundwater via the Santa Ana River.


3 thoughts on “Hidden in a Hill – Perris Hill Reservoir

  1. I think it’s genius. Very good use of space. Sounds like its better being housed under ground in cooler spot than above ground. Win win

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