Recapturing backflushed pool water - Community Action

Sunset, Sept, 1990

Backflushing a pool is the only way to remove all the hair, oils, dirt, and other debris that clog filters and it helps keep the water clear and chemically balanced, But at a time when many communities are having their water rationed, backflushing into a sewer seems to fly in the face of water conservation.

Bob Sprague, the manager of a midsize (120,000-gallon) community pool in San Jose, California, felt that there must be a way to keep the pool clean and clear without wasting water. He came up with a simple solution that can be scaled to work with a pool of any size. Owned by the 300 families who make up the Park Wilshire Improvement Association, the pool Mr. Sprague manages has a diatomaceous earth filter system that had to be backflushed two or three times a week during months of heaviest use pumping an average of a thousand gallons of water into the sewer on each backflush. To recycle the water, Sprague installed a pair of gate valves in the backflush line and linked three 400-gallon holding tanks to the line. Now the first burst of backflushed water carries the bulk of debris and dirty diatomaceous earth down the sewer. Then, after the initial 200 to 250 gallons have passed through, Sprague diverts the water into the tanks. A single line of 4-inch PVC pipe fills the tanks simultaneously. No valves regulate the flow into the tanks, but small pipes between them ensure that the water level will be the same in all three. Even though most debris is flushed in the first 200 gallons or so, the remaining 750 gallons still contain some debris; this must be removed before the water can be put back into the pool. To capture larger remaining debris, nylon filter bags fit over the inlets to the tanks. Also, water stays in the tanks overnight to allow fine sediment to settle to the bottom. A small pump returns most of the remaining water to the main filter. About 4 inches of sediment-filled water remains in the tanks, and this soupy mixture is removed periodically. Almost 750 gallons of water are saved after each backflush, and water has been filtered three times before it returns to the pool. The net savings is 5,000 to 6,000 gallons a month during the summer. c