How much rain falls on your roof every year? More than 34,000 gallons like many 1,500 square-foot-homes in Portland, Or.? Even more? Imagine the benefits of capturing this rain and using it for your water needs. Many Americans are doing just that through rainwater harvesting.

“People have been harvesting rainwater for thousands of years,” explains Jason Carlson, staff chemist at UL Water Systems, which tests and certifies rainwater harvesting components for potable end use. “It's kind of like solar where you get free energy from the sun. With rainwater catchment, you're getting free water from the sky, but, like with solar, you have to pay to catch it. And today, we have the scientific knowledge to help ensure that the components used in the rainwater harvesting system don’t introduce toxins into the water, and that the system filters out pathogens such as bacteria and protozoa.”

In addition to being able to lower – or even eliminate – your water utility bill, rainwater harvesting offers numerous additional benefits, including the below, from the Texas Manual on Rainwater Harvesting:

  • Used at its source, eliminating the need for a large-scale and costly distribution system
  • Provides freshwater when other sources (like groundwater) are unavailable
  • Has zero hardness, extending the life of appliances
  • Superior for landscape use; plants thrive on it
  • Reduces flow to storm sewers and the threat of flooding
  • Helps utilities reduce peak demands during summer months

Plus, Carlson points out, storm water roof runoff, which rainwater harvesting captures and treats on-site, can have a negative impact on fresh and saltwater organisms if not collected or treated. “Studies by the Department of Ecology in the State of Washington estimate that 88 percent of the zinc, 60 percent of the cadmium, 20 percent of the arsenic and 10 percent of the copper released within the Puget Sound basin could be associated with roof runoff.”

How It Works

According to “Rainwater Catchment Systems,” a whitepaper by UL, rainwater harvesting systems typically consist of a:

  • Collection area – usually a building’s roof.
  • Pre-filtration – devices like screens and gutter guards to keep debris out of the system and first flush diversion devices (for diverting water from the initial rain fall, which typically is more likely to contain roof debris and dirt).
  • Transport system – gutters and downspouts that direct the water into the holding container; later in the process, pipes, pumps and valves move water from the holding container to where it’s needed.
  • Container – a large cistern or tank to collect and store the water.
  • Final treatment system – micro filtration and ultraviolet (UV) or chemical purification is required before water can be used for drinking.

How to Get Started

First, Carlson advises, check local building and plumbing codes that govern rainwater harvesting, often found on your municipality’s website.

“Large scale rainwater harvesting is more or less against the law in Colorado,” Carlson points out. “But in many cities, it’s legal and incentivized.”

For instance, Santa Fe County, N.M., and Tucson, Ariz., require rainwater harvesting on new buildings, and Tucson homeowners can qualify for up to $2,000 toward a rainwater catchment system on their existing home. The City of San Diego Public Utilities offers $1 for every gallon of rainwater storage capacity up to 400 gallons per property, Tuolumne County Resource Conservation District offers $0.30-$1 per gallon harvested, and many other utilities also offer rebates. Check into financial incentives from your city, county, and utility.

The next step is to figure out how much water you can harvest by seeing how much rain you receive a year at U.S. Climate Data, then enter it and your roof size into this calculator.

Consider how advanced you want to go. The simplest, a water barrel under the downspout with overflow device and hose/spigot to access the water, can be put together for $40-$100 and used for irrigation; the State of Maryland offers a step-by-step guide. On the high end, you could go with a system that harvests nearly all rainwater off the roof, treats it and pipes it into your house. This is what an estimated 30,000 to 60,000 people in Hawaii do out of need, according to Guide on Rainwater Catchment Systems for Hawaii – and many people in the U.S. and around the world are setting up these systems too. A professionally installed, comprehensive rainwater catchment system that meets plumbing codes and provides all the water needs for a typical single-family home often costs between $8,000-$10,000, according to the Texas Water Development Board, with partial systems costing less.

“Be sure to involve a licensed contractor for anything more complex than a rain barrel,” Carlson urges, “so that you follow all local building and plumbing codes and only purchase components that are NSF 61 or P151 approved, which ensures they are compatible for use with rainwater to be collected for drinking water.”

You’ll also be able to get an accurate cost estimate that way and then can calculate how long a system would take to pay for itself (in purely financial terms).

Carlson urges families to look into rainwater harvesting, even if only at a basic level. “Even if it doesn’t rain that often, if you can collect a few thousands gallons in a rain event, you could store enough for weeks or months between rain events. And it’s fun. People are passionate about it, and you’re helping preserve a finite resource.”