By Giles Blunden
Special to The Citizen
As the drought lingers on in North Carolina, there is much discussion about how to more effectively use our water. The reality is that even in a drought year, the Piedmont still got 32 inches of rain. In many parts of the country, this would be considered a huge amount. Los Angeles, for instance, averages about eight inches of rain per year and in a drought year gets four.
By conscientiously watering our gardens with rainwater and storing more of it, we can reduce the impact of our drought. Last summer, it was disheartening to see my flowers and vegetables wilting in the 100 degree heat. Fifteen hundred gallons of stored water provided by a cistern would have made my garden a much happier place.
Catching the relatively clean water from roofs is a time-tested tradition and local use of rainwater cisterns has grown steadily over the past few years both in new homes and schools. There is a lot more water available than you might think.
In the North Carolina Piedmont, an inch of rain is a common occurrence; an average thunderstorm will produce as much. One inch of rain can produce 62 gallons of rainwater for every 100 square feet of roof – enough to fill up an average rain barrel. A modest 1,500-square-foot roof can fill up 15 rain barrels with that one inch of rain. That’s almost a thousand gallons of precious water. The next step up from a rain barrel is a cistern.
We don’t have to search far to find local examples of homes using cisterns.
Historically in the South, cisterns were buried brick vaults with a hand pump. When I arrived in rural Tennessee in 1960, I lived in a pre-Civil War home that had an underground cistern with a hand pump outside and another in the kitchen. Last fall, I visited Ocracoke and noticed the remains of many old brick cisterns. Cisterns went out of fashion when deep wells with electric pumps and municipal water systems became the norm. Droughts and increases in population have begun to stress our municipal systems, and we have come to realize that ground water is a limited resource. The cistern is perhaps the best solution for increasing our personal supply of water.
Cisterns come in all shapes and sizes, manufactured from plastic, metal or concrete. They are installed above and below ground, can be fully automatic and pressurized or can be a simple hand-pump or gravity system. The old homeplace cisterns were put in the ground for good reasons. Gravity is perhaps the best reason; water flows downhill and getting it from the roof to an underground tank is pretty straightforward. The downspout from the roof to the cistern provides a place to install filters and debris ejectors. Temperature is the other great advantage. The average underground temperature below three feet is 55 degrees year round. Storing water at a cool 55 degrees solves the problem of freezing; it also reduces algae, which needs light and warm temperatures to grow.
Pre-cast concrete tanks are ideal for underground installation and are readily available in the 1,000-to-1,500-gallon range. Molded plastic tanks are also an option. However, the concrete tank has distinct advantages. Empty plastic underground tanks have a tendency to “float†out of the ground when the earth is saturated, and concrete tanks are considerably heavier. Instructions for plastic tanks of 1,000 gallons or more recommend the tank maintain 25 percent capacity to act as a ballast to prevent it from popping out of the ground. As a result, only 750 gallons of water are available out of 1,000 gallons of stored water. Many plastic tank manufacturers also recommend a mix of sand and fine stone as backfill since the tank is more delicate – an additional expense. Lastly, the polyvinylchloride many plastic tanks are made of poses environmental liabilities during the manufacturing process.
I recommend a concrete tank. Similar to a septic tank, it is mass produced and takes relatively light equipment to install. A 1,500-gallon tank can be purchased and installed for about $1,800, assuming the site can be easily accessed by truck.
The one disadvantage of an underground tank is the need for a pump and a hose. For gardening and outdoor water play, small submersible pumps can be used and are readily available at your local building-supply store. These pumps are often used as sump pumps in basements or portable pumps on construction sites. Many pumps are made with a hose connection. Place the pump in the tank and plug it into the nearest outside GFI outlet. There are many ways to improve this system using switches, timers, wiring and pressure tanks; however, plugging and unplugging the pump when you need water is the easiest and most trouble free.
Keeping debris out of the tank is important in maintaining high water quality and in keeping tank cleaning to a minimum. The best filtering medium is sand; it blocks large debris like leaves and catches the finer contaminants from your roof. The sand develops an active micro-organic layer that neutralizes the bacteria and many of the pollutants and contaminants.
In addition to gardening, the North Carolina plumbing code allows cistern water to be used for toilet flushing, clothes washing and generally anything except personal hygiene and food preparation. Only 50 percent of water use in the average household is for personal hygiene and food preparation, so a lot could be provided for with a cistern. For health and safety reasons, there are very strict rules about keeping potable and non-potable water separated and requirements for clear signage warning that the cistern water is not drinkable. Using rainwater in this way is a possibility but it involves re-plumbing your house at a sizable investment. If you choose this option, hire a licensed plumber.
Remember: In North Carolina even a drought year brings about 32 inches of rain. This much rain on a 1,500-square-foot roof produces about 30,000 gallons of water a year – enough to fill a 1,500-gallon cistern roughly twice per month! That’s a lot of tomatoes.
For more information, the Internet is your best source. One of the most informed sites is Oasis Design (www.oasisdesign.net). For a diagram of a simple cistern system and resources for local conditions, see www.blundenstudio.com or www.braewater.com. A good source for specialized hardware is Stark Environmental (www.starkenvironmental.com).
Giles Blunden is an architect and president of Blunden Studio, PA. He is a LEED (Leadership in Energy and Environmental Design) certified professional and has been designing green homes in the Triangle for over 30 years.
For smaller scale rain water harvesting applications be sure to find rain barrels which offer a mesh mosquito guard, and also look for barrels which have an overflow valve function to allow the excess water to flow out of the rain barrel and away from your foundation. Hooking a drip hose to this valve is a great way to give your garden or flower bed a constant source of moisture.
Also for smaller scale rain water harvesting applications be sure to check out the very affordable rain barrel pump made exclusively for rain barrels. http://www.rainbarrelpump.com