|How to Choose and Use a Home Rainwater Catchment System|
|Wednesday, 07 September 2011 00:00 | Written by Aaron Lada, Ph.D. | Article|
How big is your H2O footprint? With water shortages a growing concern, it makes sense to calculate and then try to reduce it. Once you do, a rainwater catchment system will guarantee that the water you do use comes directly from the sky without the environmental burden caused by relying on your local water treatment plant.
The simplest rainwater catchment systems provide water for irrigation and washing cars, patio furniture, etc. The next level allows for non-potable indoor uses like toilets and laundry. The most complex can provide water suitable for any use—including drinking. Here’s what you need to know to choose and use one.
How They Work
The final components deliver water for use. Simple setups have a hose or faucet attached to a collection tank; more complex ones direct water into a pump and then possibly through filters and a sterilization system. Roof washing devices are available that divert the first 10-15 gallons of rain away from the collection tank, keeping the majority of contaminants such as animal droppings, pollen and soot out of the system.
No clear regulations are available for using untreated collected water on food plants. It may be best, however, to avoid using the water on vegetable gardens and fruit trees, or at a minimum to use water only at the base of the plant to avoid getting contaminants on any edible parts.
Non-Potable Indoor Use
After water is collected from the roof into the cistern, it moves into a pump that generates the pressure to move the water through a separate plumbing system. Filtration can occur in the downspouts, inside the tank, or after water leaves the cistern. Plastic and metal cisterns are available at a cost of $500-$2,000, depending on size.
Potable Indoor Use
After water is collected in the cistern, a pump moves it to an indoor storage tank. Then the water is treated using filters, ozone or UV irradiation to make it safe to drink. Finally it is piped throughout the house. Local plumbing codes vary, but most require a backflow device that prevents the water from flowing back into a public water supply.
Choosing a System
For a potable system, determine the total water needed using the following calculation. Assume 40 gallons of water used per day per person. Next, determine the square footage of the roof. On average, each 1000 square feet can store 550 gallons per inch of rainfall. For example, a household with two people would require 29,200 gallons per year. With a 1000-square-foot roof, it would have to rain 53 inches a year to provide enough water. Of course, a larger roof would require less rain.
For most, rain harvesting cannot fulfill all water needs. However, diverting rainwater for outdoor and indoor non-potable uses will lower your water bill while helping reduce demand on public water supplies as they become increasingly stressed. It also limits the amount of runoff into streams and storm-drain systems—minimizing your environmental impact. All in all, a water catchment system is an easy and low-cost way for you to live a more sustainable existence.
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