Water & Drought

How do I dechlorinate pool water to irrigate trees?

Q: In your column, you mention dechlorinated pool water. If I get a little more water in my pool, I may need to drain some out. How do I dechlorinate the water, and could I use it to water my redwood trees? – Charlie Mckenzie, Fair Oaks

A: Using pool water for landscape irrigation is pretty easy. Chlorine naturally dissipates into the air and out of your pool water when exposed to sunlight. The process usually takes less than a week.

If you plan on using pool water to irrigate your trees, don’t add any more chlorine to your pool. After four or five days, test the water. When its chlorine level dips below 0.5 parts per million, the water is safe for most trees. (You should follow this same procedure before emptying the pool, too.) At that low level, the water will not smell like chlorine.

Another way to remove chlorine from pool water: Put it in a big bucket or other large container, place it uncovered in a sunny spot and leave it outdoors. After a week, all the chlorine will have dissipated into the air.

Redwoods usually are OK with dechlorinated pool water, but some trees are very sensitive to chlorine. Among the trees that may have a negative reaction to pool water are most varieties of maple, box elder, ash, crabapple, dogwood, horse chestnut, mulberry, pin oak, sweet gum and yellowwood. Avoid irrigating those trees with pool water unless it’s been thoroughly dechlorinated.

Your tree will tell you if it’s sensitive to chlorine. Signs of chlorine poisoning look similar to frost burn; leaves turn yellow or brown. Tips of branches may appear brown or “burned.” Flushing the soil with non-chlorinated water will leach out the toxin (and also irrigate the tree again).