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New Mexico State University

New Mexico State University

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Water from Air Conditioner Too Harsh for Most Plants

LAS CRUCES -- With the onset of fall, many New Mexicans are draining their evaporative coolers in preparation for winter. Water-wise residents who use the leftover water on their gardens may actually be harming their plants, said a New Mexico State University horticulturist.

"Some homeowners use anti-algae and anti-fungal products in their evaporative coolers to keep the system clean," said Curtis Smith, with NMSU's Cooperative Extension Service. These products may contain copper, which is toxic to many plants; or salt, which causes injury in high concentrations.

"Another important thing to consider is that, as water does its job of cooling the air, it evaporates," Smith said. "Any dissolved minerals in the water are left behind in the cooler's pan."

While plants need minerals, such high concentrations in water drained from evaporative coolers may cause injury.

New Mexico water usually contains calcium and, in some locations, sodium, Smith said. Too much of either can be harmful to plants.

"Some of our native plants can tolerate high levels of calcium, but few can tolerate a lot of sodium," he said.

In gardens with plants that have proven a tolerance to high mineral levels, draining water from the air conditioner shouldn't pose a problem. However, use the water on flowering plants, not on food crops, Smith advised.