Rainwater Harvesting

Rainwater harvesting is another way to reduce the amount of potable water used.   In 2009, the N.C. Legislature passed State Law 243, authorizing changes made in the plumbing code to facilitate the use of cistern water in both residential and commercial buildings.  The law prevents any state, county or local building code or regulation from prohibiting the use of cisterns for these applications.

The N.C. Building Code Council has added Appendix C-1, Rainwater Recycling Systems, which has new requirements for rain water connections, collection reservoir, filtration, overflow and makeup water for cisterns used for flushing toilets and urinals.  These requirements protect public health by making the water easily identified as non-potable.  Although Appendix C-1 shows a delayed effective date of Jan. 1, 2011, subsequent ratification of State Law 243 made the new plumbing code revision effective immediately.

Harvested rainwater can be collected from a building’s roof in a rain barrel or cistern, allowing it to be saved and used during dry periods.  Rain barrels (usually about 60 gallons each) are more appropriate for residences and small buildings where there is not a high demand for irrigation.   Cisterns are larger, may be buried in the ground, usually have pumps to deliver the water back out, and are more appropriate for larger buildings and those with a higher water demand, such as a large yard or garden.  A 1” rain event will produce 600 gallons of rainwater per 1,000 square feet of roof; a ¼” rain event is enough to fill the rain barrels on a typical American home.

Many local governments and businesses offer rain barrels for sale through their city government offices, solid waste department, community centers or during special sale days.  Click here for a quick fact sheet on how to build and install a rain barrel or divert roof runoff directly into a rain garden.

Cisterns can be sized to meet the irrigation or other reuse needs at a site and have the added benefit of helping to control stormwater runoff.  Stormwater runoff can harm water quality by picking up contaminants as it drains over roads, lawns and other surfaces before entering our surface waters through ditches and storm drains.  Reducing the speed and volume of stormwater from roofs reduces this contamination.

The N.C. State Legislature building has three 18,000 gallon cisterns buried on site.   Captured rainwater and air conditioning condensate are filtered, stored in the cisterns, and used for all the decorative fountains and irrigation needs at General Assembly complex.   Read more about this stormwater collection project.

Resources
How to Build and Install a rain barrel or rain garden
Rainwater Harvesting at NCSU
Urban Waterways – Permeable Pavements, Green Roofs and Cisterns

Case Studies
UNC Chapel Hill - Rainwater Cistern Use
N.C. Aquarium at Pine Knoll Shores Cistern Fact Sheet
N.C. Legislative Building - Stormwater Collection Project

Videos
How to Build a Rain Cistern – N.C. State Cooperative Extension Services
Construction of N.C. Museum of Art’s Cistern