Rainwater catchment systems in Hawaii

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Tens of thousands of residents in Hawaii rely on catching rainwater for their household water needs. A majority of these residents, as it turns out, live on the Big Island.

If you are unfamiliar with catchment tanks, it helps to know that there are no official government regulations that oversee the safety or operation of individual water catchment systems. It’s the responsibility of the homeowner or resident to know exactly what’s involved in maintaining a catchment tank for collecting water used for bathing, washing, flushing, laundry, irrigation, and in some cases, drinking.

In Hawaii, a galvanized roof offers the traditional surface for catching rainwater. If you live in an older home, be sure to test your home’s exterior for lead-based paint. Gutters made of PVC are typical for catchment systems. These are installed in a continuous downward slope that leads into the tank. The downspout is angles such that the water completely drains out, as opposed to other configurations that could leave standing water inside. It can’t be overemphasized enough that gutters must be clear of leaves and debris, otherwise the quality of your water will be affected, and also, mosquitoes will find the perfect breeding site.

To divert the initial flow of water away from the tank when rain starts to fall, automatic first-flush diverters are installed. This helps to flush away contaminants that may have collected on the roof.

The tank itself is more often than not made of corrugated metal. Liners for the tank must be FDA approved. Make sure your cover Ferroconcrete tanks can withstand earthquakes, as well as reduce the acidity content of acid rain. Some resourceful architects in Puna have built their home on top of the concrete tank, which provides a slab surface for the floor.

Most households on catchment use about 80 gallons a day for flushing and 65 gallons a day for bathing. Adding chlorine to your tank will kill most bacteria and fungi, but not all, like those that cause Giardia.

Keep 1 part per million dilution of chlorine in your water at all times by adding two ounces of unscented household bleach (6% strength) per 1,000 gallons of water monthly or biweekly depending on the frequency of rainfall.

County water can be kept on hand for drinking, cleaning food and brushing teeth. Some homeowners install high-tech filtration systems for drinking water.