Water flowing into rain barrel

How Rainwater Catchment Can Help in Drought Areas

Did you know that one inch of rain falling on 1,000 square feet of a roof amounts to 640 gallons of water? That’s a significant amount of water—more than most households use in a day—and evidence of the fact that in a typical year (and in a temperate climate), thousands and thousands of gallons of available water are running off your roof.

The most common term for collecting water for household use these days is “rainwater catchment.” While still rare in the United States, it is quite common in other parts of the world, notably in the Caribbean. In fact, GAF, sells TOPCOAT® Membrane WOB (without biocide), a specially formulated coating for use in rainwater catchment systems, and the lion’s share of it is sold there (and I am never invited to check on it, unfortunately). However, partly out of necessity and partly for reasons of conservation and sustainability, rainwater catchment is becoming more common in the United States.

Consider the fact that you’re watering your lawn and flushing your toilets with drinking water, and think about using rainwater for those times instead.

Rainwater catchment doesn’t have to be complex: you can start with a rain barrel and catch water for the lawn. More advanced systems incorporate a device called a first flush diverter. This diverts the rain that falls for the first few minutes away from your catchment system or barrels in order to “wash” the roof of pollen and other buildup that has accumulated since the last rain. From there, additional advances include filtration, treatment, and underground storage cisterns.

To really get where we need to be with rainwater catchment, significant plumbing work is required. That’s because separate systems for drinking water and rainwater would be needed for most homes. However, there has been some progress in this area, including the development of a standardized piping color (purple) for irrigation water.

Industrial users can benefit from rainwater catchment systems as well. A common use of rainwater is for cooling tower systems, which rely on evaporative cooling and thus require large amounts of makeup water to replace that which has evaporated. A rainwater catchment system on a large commercial roof paired with storage tanks—often mounted directly on the roof or sometimes buried under a parking lot—can easily supply this makeup water. And again, why use drinking water for this?

Have you experienced a water shortage in your area? Have you looked into rainwater catchment or other methods to use the roof as a water-savings asset? The day may come for more of the country as Net Zero homes also try to achieve Net Zero water.

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