Rain, Rain Stow Away - Water Harvesting Systems

As mentioned in the Living Building Challenge Imperatives, water harvesting systems play a vital role in any truly sustainable home design. It’s a simple idea, really: Set up a system to catch the rain before it hits the ground. So long as you live in an area that enjoys more than eight inches of annual rainfall, your rainwater harvesting stands a good chance at success.

In their simplest form, catchment systems channel rainwater from a home’s roof through a medley of gutters and pipes into a storage tank. To ensure proper flow-through and avoid standing water, gutters need sufficient incline and strength enough to withstand peak flows. The anchor of the system – the storage tank – must boast a cover to guard against mosquito breeding, evaporation, algae, and contamination. It’s crucial to maintain and clean the system on a regular basis.

Your catchment system can be as simple or complex, as cheap or expensive as you want it to be. On the low end, construction can incorporate inexpensive materials sourced locally and still do the job well. The real factor impacting yield – other than, of course, precipitation – is the size of the system’s footprint. The broader the area, the bigger the volume. Here’s an equation to estimate how much water you’ll capture: annual precipitation (mm per annum) x square meter of catchment area = litres per annum yield. For example, a 200-square-meter catchment collecting 1,000 mm of rain annually will yield 200,000 litres per year.

Depending on the intended uses of the harvest, water treatment may or may not be necessary. If your goal is simply to provide your garden with an irrigation source during the dry season, then you’re good to go. Adding a sediment filter and an activated-carbon filter allows usage in toilets, washing machines, and most other external uses without fear of pipe damage, odors, or stains. Combined, these account for about half of a home’s consumption.

If you want to drink or shower in your bounty, include a high-intensity ultraviolet sterilizer to kill harmful microorganisms. Also, a general rule of thumb is that the first rain after a long, dry spell should not be gathered because it will contain bird droppings, sediment, moss, and the like that it washes off the roof.

Before you dive into rainwater harvesting, be sure to check state law as pertains to water rights. Believe it or not, some states "own" all water rights, leaving land owners in a lurch. As an example, in Colorado, you can only harvest rainwater from your roof after first securing a permit. The idea behind such policies is that the harvesters are "stealing" water that would naturally go into the watershed where it would be used by everyone.

That’s not a global trend, though. In Santa Fe, New Mexico, Bermuda and the U.S. Virgin Islands, the law actually requires all new construction to include catchment systems for residents. The UK enjoys a similar statute in its Code For Sustainable Homes which encourages the inclusion of large underground tanks in new construction projects. The idea is that these harvesting systems would source the water for toilets, laundry, and gardens in order to achieve that 50% reduction in usage mentioned above.

If you pursue rain catchment, do so knowing that you are helping both the micro and macro water systems. Your home’s consumption will be lowered, but you will also lift some of the burden from your region’s sewage processing system, particularly during heavy rainfalls that overload a plant’s capacity. Yet another win-win for the eco inclined.

About the Author
Brynn Alexander writes for Homeguide411.com, a directory of home professionals and an in-depth resource for home owners and home buyers. Visit the Homeguide411.com blog where you can read useful articles such as Water Harvesting Systems.