Doug Pushard, an expert in rainwater catchment systems who shares his know-how at HarvestH2O.com, believes that homeowners capture rainfall for two reasons—either to make the most of a precious water resource in states with low seasonal precipitation or to control stormwater runoff in states with high precipitation.

It’s also an easy way to make a dent in household water and sewer bills. Capturing and managing rainwater provides an environmentally sound alternative to wasting precious tap
water pulled from diminishing underground reservoirs, and can replace some or all of a home’s water needs, depending on the system. Rainwater is also better for nourishing lawns, plants and gardens. “People want to use rainwater instead of city water in their yards because they understand that city water carries chlorine, which is not great for plants,” Pushard explains.

The amount of water used by residential irrigation is significant. According to the U.S. Environmental Protection Agency’s (EPA) Water Sense Program, an American family of four uses 400 gallons of water a day, including 30 percent of it outside. More than half of that outdoor water is used for lawns and gardens, with the rest sprayed on cars, in swimming pools and on sidewalks and driveways. Collectively, nationwide landscape irrigation totals more than 7 billion gallons per day.

Water Calculations

In its simplest form, rainwater harvesting involves little more than placing rain barrels—with capacities from 55 gallons to several hundred gallons—under a home’s downspouts. Popular models can be purchased from home improvement stores, or county extension classes teach how to make one from inexpensive parts. Online research shows the various styles available; most have a spigot at the base for attaching a hose or filling a watering can.

The larger capacity, more sophisticated systems use storage cisterns than can hold thousands of gallons of water below ground. These employ pumps that move the water to sprinkler systems or other points of use.

For these more complicated setups, Pushard recommends engaging professional help, adding that below-ground systems will capture excess water year-round, even in climates where temperatures drop. “In northern New Mexico, where I live, we get almost one-third of our precipitation in the winter,” he says. “If you have a below-ground system, you can capture that; with an above-ground one, you can’t, because the tank or fittings would freeze and burst.”

The formula for determining the maximum amount of water available to capture is related to roof size. Multiply the square footage of the roof times the local annual rainfall (found at Tinyurl.com/73enzjx), and then multiply the result by .623 gallons. That .623 factor is “how many gallons are in an area of one square foot by one inch deep of rainwater,” according to one of Pushard’s online tutorials.

Not all roof materials are created equal. On the high end, tile, metal, concrete or asphalt roofs have a 95 percent runoff efficiency; gravel roofs, 70 percent; and grass roofs, 17 percent, so factor that in, too. Pushard recommends always going with a bigger tank, if possible, to avoid having to add more water storage later.

Think Big

Rainwater harvesting works as an effective irrigation device, but it needn’t be limited to outdoor use. One of the easiest—and most useful—places to direct captured rainwater is toilets. Citing bathrooms as a home’s biggest water user, the EPA notes that a single toilet can use 27 percent of household water. “It’s ludicrous that we use drinking water to flush toilets,” says Pushard. To use stored rainwater instead, run a new plumbing line to the rainwater storage tank and install a pump that activates when the toilet flushes.

Rainwater can supply sink faucets, as well, but counting on rainwater to be the sole source of all household water requires a substantial investment and a filtration, purification and UV light system to make the water drinkable. When capturing rain for potable uses, roofing material becomes more important: Unpainted metal and tile are preferred, because these will not leach chemicals into the water that are difficult to remove.

In terms of overall cost, the simplest rainwater collection systems will cost a few hundred dollars (less than $100 per barrel), while a whole-house system will cost tens of thousands. However, Pushard points out, rainwater harvesting can be a lifesaver with water shortages becoming a new norm in many states.

Brita Belli is the editor of E-The Environmental Magazine and the author of The Autism Puzzle: Connecting the Dots Between Environmental Toxins and Rising Autism Rates.