There are specific considerations associated with designing an active rainwater harvesting system that will be located in a forested area and/or an area prone to wildfires. Storing water in fire-prone areas increases wildfire resilience because it can serve as a backup water supply in case of an emergency. In many cases, storing water in fire-prone areas is recommended by local fire departments, and insurance companies give reduced rates to properties that have onsite water storage.
People have been using rainwater harvesting systems to store water for fires for a long time. Interestingly, Thomas Jefferson installed two cisterns on the northern side of his home for fires and two cisterns on the southern side of his home for laundry and gardening. Jefferson first mentions these cisterns in some construction notes in 1771-1772. However, the official Monticello website indicates that Jefferson’s cisterns were never completely watertight and only two reliably collected and held water over the years. Even so, this piece of history shows that rainwater harvesting has been a part of America’s past just as it will, in all likelihood, be a more prominent part of our future.
Today, rainwater harvesting systems are much more reliable than the cisterns constructed at Thomas Jefferson’s home. If you are thinking about installing a rainwater harvesting system to build wildfire resilience, consider asking your local fire department to conduct a free walk-through with you. They can help you address concerns associated with clearing and ensure the site is ready before your cistern arrives. The following blog post provides some information about designing a rainwater harvesting system for fighting fires.
Codes And Standards For Designing Rainwater Harvesting Systems in Fire-Prone Areas
When designing a rainwater harvesting system in a fire-prone area, ensure your design meets the local requirements for clearing and water storage. It is also important to ensure that firefighters are able to connect their equipment to your tank. Finally, rainwater tanks designed for the purpose of fire protection should be compliant with the standards outlined by the National Fire Protection Association (NFPA). Some of these standards are described below.
NFPA 20
NFPA 20 describes the requirements for installing pumps to “ensure that systems will work as intended to deliver adequate and reliable water supplies in a fire emergency.”
NFPA 22
NFPA 22 outlines the requirements for on-site storage tanks that supply water for private fire protection.
NFPA 25
NFPA 25 describes the inspection, testing, and maintenance of water-based fire protection systems.
NFPA 13
The NFPA 13 Standard for the Installation of Sprinkler Systems describes the requirements for using rainwater, recycled, or reclaimed water for fire protection systems. The water used for fire protection must pass certain water quality standards to ensure that it does not damage fire fighting equipment. The pH of the water should be tested in accordance with ASTM D 5464. In addition, water quality testing for filterable solids should be conducted per ASTM D 1253, and turbidity per ASTM D 6698.
Dual-Purpose Rainwater Tanks
A dual-use rainwater tank reserves a portion of stored water for fire fighting and a portion for other needs. A dual-use tank will have two outlets plumbed into the tank. One outlet, which is for accessing fire protection water, will be located just above the bottom of the tank. The other outlet, which is for accessing water for typical site needs, will be plumbed at a higher elevation on the tank.
Requirements for dual-purpose tanks are discussed in NFPA Standard 22.
Underground Tanks vs. Above Ground Tanks
According to the American Rainwater Catchment Systems Association (ARCSA), most fire departments prefer underground rainwater harvesting systems because they allow for easy pumping and are less susceptible to fire damage. However, above-ground tanks (metal or concrete) can also be effective. Above-ground plastic/polyethylene tanks are not resistant to fire.
Drafting or Fire Department Connection (FDC)
The FDC allows the local fire department to connect their equipment to your tank. Thus, drafting or Fire Department Connection (FDC) requirements are based on local regulations. An average FDC is a 4-inch pipe with a shutoff gate valve. It is important to clearly indicate FDC locations with signage.
Other Considerations
- Portable pumps should be easily accessible to provide pressurized flow for firefighting.
- Place tanks on the leeward/downwind side of a building or in an area cleared of vegetation.
- For above-ground tanks, use fire-resistant materials such as metal or concrete.
- Bury pipe underground when possible.
- Install fire-resistant metal fittings and couples.
- Install backflow protection if tanks have a potable water connection.
- Remove fire-prone debris from catchment surfaces, gutters, and prefilters.
- In the case of a wildfire evacuation, unlock the tank tops and ensure the location of fire tops, portable equipment, hoses, and couplings are clearly marked.