How Can I Harvest Rainwater to Use in My Home?
On average, you will flush the toilet nearly 140,000 times in your lifetime. With a typical toilet using 2 gallons per flush, you will end up employing 280,000 gallons of water to flush away your bodily waste. In most cases, that’s water that has been filtered, cleaned, and treated at an ever-increasing expense. Wouldn’t it make sense then to use water that is untreated and not fit for drinking — such as rain water that comes off your roof?
With drought conditions growing more frequent in many parts of the country, the idea of harvesting rainwater sounds like an ideal way to lower water use and help conserve valuable drinking water. The creation of such a system for non-potable water your home could range from simple gravity-fed systems to storage systems that have to contend with cold weather, indoor storage, and pumps.
These systems are not just limited to rural or suburban use. Work at Drexel University in Philadelphia shows that “a three-person family in a home with the city’s average roof size would have enough water to cover over 80 percent of its flushes throughout the year simply by diverting their downspouts to collect stormwater.”
How It Works
Your roof can collect an awful lot of rain in a single 1-inch rain storm. Consider that:
- 1 gallon = 231 cubic inches.
- 60 gallons = 13,860 cubic inches
- A roof area of 13,860 square inches or 1155 square feet (25 x 46.2) will easily fill a 50-gallon barrel when it rains 1 inch.
Additional system requirements:
- Your rainwater tank must be vented in order to allow air to escape/enter the tank as volume fluctuates.
- Vent pipes must have some sort of screen cap to keep out insects and other pests.
- The tank must have an overflow pipe. This allows excess water to drain away from the system. Landscaping to take advantage of this feature will prevent overflows from becoming a problem. Overflow pipes also must have some sort of screen cap to keep out insects and other pests.
- Avoid contamination with drinking water. Non-potable water cannot cross-connect with drinking water. Some local codes may require an air gap to reduce the threat of contamination. In this case, you can just swap the flex line to the toilet from your rainwater system’s shut-off valve to the potable shut off valve in about five minutes. Others may allow you to install a backflow or check valve on the potable supply line to prevent water flowing backward from the joint with the rainwater line.
Your geography and home design will have a big effect on how you should collect and store your harvested rainwater. For example, if you live in a northern state, you’ll need to store the water where it won’t freeze. Otherwise, you won’t be able to use it if it freezes into a solid block of ice.
Likewise, mounting a large water tank over your bathroom to take advantage of gravity to feed water to the toilet means installing some extra support for that tank. Water is heavy: 8.33 pounds/gallon. A 50-gallon barrel weighs over 400 lbs when it’s full.
Another alternative is to install an underground cistern below the frost line. Plastic underground tanks with 1,000 gallon capacities cost around $1,000. Rainwater would collect in the cistern tank and then need to be pumped to supply toilets and washing machines.
But the major problem with rain runoff from your roof is it contains dissolved air pollutants from factories and highways, and it carries dust, pollen, molds, decaying plant matter, and particles from your roofing and gutters. When it starts raining, dirt and debris usually get washed off the roof during what’s called the “First Flush.” If it’s not removed, this muck can also clog pipes and pumps. By building a trap and diverter out of PVC pipe, all this muck gets removed from the rain water before it’s collected in your rain barrel or other storage. You can build one of these yourself for under $50. Additional filtering with fine screens is also a could idea.
Challenges and Opposition
Until only a few years ago, neither the Uniform Plumbing Code (UPC) nor International Plumbing Code (IPC) directly addressed rainwater harvesting in their potable or stormwater sections. Lack of code guidelines led to confusion as to what constitutes harvested rainwater, greywater, or reclaimed water:
- Greywater – Untreated wastewater that hasn’t come into contact with sewage or blackwater. Greywater includes used water that contains soaps and detergents from bathtubs, showers, and washing machines.
- Reclaimed water – Sewage water that’s been filtered for solids and cleaned of some impurities (think sewage lagoon water) to be used for toilets, urinals, and trap seal primers for floor drains and floor sinks.
- Harvested rainwater – Stormwater collected from a building roof, stored in a cistern, and disinfected and filtered before being used for toilet flushing. It can also be used for landscape irrigation.
As of 2012, the UPC now allows non-potable rainwater catchment systems to supply “water closets, urinals, trap primers for floor drains, industrial processes, water features, vehicle washing facilities, and cooling tower makeup water.”
However, local building codes and authorities always have the final say. For example, the City of Cincinnati’s Chapter 1105 of the plumbing code says, “rainwater harvesting systems shall be permitted to be installed as a non-potable auxiliary water source for use in subsurface irrigation, flushing of fixtures and other non-potable uses approved in the discretion of the Director of Buildings and Inspections in consultation with MSD, GCWW and the Cincinnati Health Department.”
So, while there is change taking place to allow you to collect rainwater and reduce the clean drinking water you flush away, local authorities may be hesitant or skeptical. However, the need for this kind of adaptation is happening where regions are feeling the pain of water shortages. Arid New Mexico has become the vanguard of greywater and rainwater harvesting use inside the home.
Do you have any experience harvesting rainwater for your home? Share your stories with reusing non-potable water in the comments!