Using Car Wash Water on Plants?

Question:

I have seen dirty car wash water being used on other dirt but wonder if this could be used on plants to keep bugs off?

Kate from Camden, SC

Answer:

Kate,

This is a great question and at first glance, it seems like a good way to conserve water. I have no doubt that recycled water from washing your car would work to keep bugs off plants; unfortunately, I see a major problem with the detergent. Household soap and detergents that use sodium, chlorine and boron (as in Borox) are harmful to plants, either on contact, or after building up in the soil over time. High phosphate detergents can also be a major source of water pollution. Home remedies for the garden calling for liquid dish soap are generally more benign as long as you use soap that contains as few additives as possible (e.g. ivory). Compared to household detergents, most car shampoos are full of toxic additives. When you think about it, they have to be. They need to be strong enough to cut through the grease, tar, gasoline, exhaust residues, motor oil, etc., that we get on our cars, and still be able to wax, polish and protect our car's finish. Keep in mind that all the dirt and grime we wash off our cars (and spray on those bugs) would also be landing on our plants and in the surrounding soil. Even "all natural" car shampoos still leave us with the toxic residues we wash off the car. If you had the right kind of small scale filter for the water (maybe you could invent one?), this hurdle could be resolved.

The average person uses 65 gallons of water to wash their car so it would be great to figure out a way to recycle this water for use at home. I'm not a big fan of washing cars in the yard or driveway, however. It just dumps more water into the sewer system, and storm water run-off is a huge source of pollution problems in most communities. Incidentally, many commercial car washes now recycle their gray water. Call around to find one where you live. Although most recycle water to reduce costs (or because they are regulated), the environmental benefits are a great bonus.

Ellen