Use rainwater management as a ‘best management practice’

By Shawn Hatley on 03/16/2006

A national campaign promotes rainwater management as a best management practice, or environmental protection practice, to achieve large-scale water conservation and water quality protection goals. Water is our most limited natural resource, so it makes sense to integrate rainwater management into your residential or business project.

Rainwater systems are a strategy to manage the water supply and stormwater at homes and businesses. Increasing water demands and costs, mandatory restrictions and water-quality concerns spur homeowners, businesses and design teams to use rainwater systems. Challenges to a water supply include low-producing wells, high irrigation demands, expensive municipal water and lack of water. Rainwater is a supplement to a water supply–whether the source is a well, spring or city–and can help meet more than 65 percent of daily non-potable demands.

With real-estate values going up, the cost of stormwater damage to your investment can decrease value tremendously and increase your liability. Rainwater harvesting can reduce stormwater runoff. Rainwater cisterns store downspout drainage and rooftop runoff during heavy rains. That reduces flooding of sewers and susceptible areas and protects water quality in streams, lakes and rivers.

Rainwater cisterns also help with fire protection. Neighborhoods and businesses use cisterns with fire hydrants to supplement water supplies in remote mountain regions. Some insurance companies recognize the practice with reduced premiums.

It’s important to understand the four components in all rainwater systems: filtration, storage, a pump system and treatment. Filtration is the first step to make sure the highest quality of water enters your storage tank. Filter water before storing it. Water storage is the most important part of a rainwater system. In selecting a rainwater cistern, consider whether water will be stored above or below ground, how much storage you need and whether you want the above-ground tank to be wooden, steel or plastic. Remember to use black or dark green tanks that are opaque to light for above-ground storage. Other tanks can allow algae to grow in the water and cause water-quality problems.

Pump systems deliver rainwater for various applications. The systems can be sized to pressurize small garden hoses or supply school buildings with rainwater to flush toilets and irrigate ball fields. Water treatment purifies rainwater to meet quality requirements. For example, irrigation systems require sediment screening to prevent clogging of spray heads. Projects that require more protection use high-efficiency carbon filters and ultraviolet disinfection for nonchemical water purification.

To calculate the cistern size, know your project water demands on a monthly basis, and then estimate the collection potential. That’s the amount of rainwater a catchment area such as a rooftop can collect based on local rainfall averages. For example, one inch of rain on one square foot of collection area equals .623 gallons of rainwater. One inch of rain on 1,000 square feet of collection area yields 600 gallons of collectible rainwater. Once you calculate the collection potential and know project water demands, calculating the cistern size is simple. Like an accounting balance sheet, simply “bank” rainfall, and subtract water demand. This method creates a monthly forecast of water supply compared with water demands. For months with low rainfall, integrate a backup water supply.

There are myths about rainwater systems. One is that the systems are expensive. Rainwater systems are available on the retail level for less than $900 and include filtration, storage, pump system and water treatment capability. A general rule for estimating costs is $1 per gallon of storage. The cost of city water is cheap, but that certainly will change.

States and cities around the country offer incentive programs for rainwater cisterns. Incentives include exemptions from state taxes on rainwater equipment, rebates and cost-sharing arrangements. A program in Mecklenburg County pays homeowners up to $3,000 to install rainwater cisterns. Another incentive is green-building programs. The North Carolina Healthy Built Homes Program gives credits for rainwater management. Rainwater management also gets credits from the U.S. Green Building Council and the National Association of Homebuilders’ (NAHB) Green Home Building Guidelines.

North Carolina is a leading state for rainwater-management developments and projects. The North Carolina state legislature building harvests rainwater and condensate from heating, ventilation and air-conditioning systems in three 18,000-gallon cisterns for landscape irrigation. The North Carolina Arboretum collects rainwater for the bonsai exhibit and to protect downstream water quality. Guilford County Schools use rainwater to flush toilets and irrigate athletic fields, and the North Carolina Museum of Natural Sciences’ Prairie Ridge Eco-station stores rain in a 1,400-gallon cistern to flush toilets in the outdoor classroom.

There are several ways to integrate rainwater management into your project. One way is simply to ask. A common response from engineering and architecture firms about why rainwater management is not integrated into projects is that clients did not ask. Once educated about the concept and its ability to protect water quality and conserve water, clients ask for it. Companies also are becoming more educated about rainwater management as it relates to drainage, stormwater permit requirements, Green Building Program credits and water-supply challenges. As long as your cistern holds water, rainwater management will go a long way toward protecting water quality and conserving valuable drinking-water resources.

[Shawn Hatley is the southeastern regional rep for the American Rainwater Catchment Systems Association, or ARCSA (, the president of BRAE (, and he practices as a LEED™ accredited professional. Contact Hatley at or (800) 772-1958.]