The District’s system includes four finished water storage reservoirs. Water flows by gravity from the North Reservoir through the distribution grid to the Central and South Reservoirs. These two reservoirs are said to float on the system. They fill and empty depending on system demands and system pressures. The four reservoirs (North, Central, South, and Salishan Standpipe) have a combined storage volume of 3,150,000 gallons. Of this total, the 1,000,000 gallons of the North Reservoir is dedicated to chlorine contact time. The remaining volume of 2,150,000 gallons is available to meet distribution system needs.

North Reservoir

All supply from the slow sand filter plant passes through the North Reservoir, which is a 1-million-gallon capacity bolted steel reservoir. The North Reservoir establishes the hydraulic grade line for the gravity zone of the system. The water level in the tank is used to start and stop the high service and intake pumps at the slow sand filter plant. The volume supplied in this reservoir provides the dual purposes of meeting chlorine contact time requirements and of providing a buffer, allowing the treatment plant to operate at a steady rate even as demands fluctuate in the system.

South and Central Reservoirs

The Central and South Reservoirs are ground-level welded steel tanks. Each tank holds 1.0 million gallons. Since the water levels vary depending on production and use rates, the tanks may provide 1.0 to 2.0 million gallons of emergency water if an earthquake occurred.

Salishan Standpipe

The fourth reservoir is the Salishan Standpipe, a 150,000 gallon tall welded steel tank located at a high elevation in the Salishan development.