Harvest the Rain
(Page 5 of 8)
August/September 2003
Adapted from Environmental Building News
If the rainwater collection and storage system is located uphill from where the water will be used, gravity-flow conveyance might be possible, but the verti cal distance between storage and use is rarely enough to achieve adequate pressure for modern household plumbing. For most rainwater harvesting systems, a pump and pressure tank are required for water delivery. Richard Heinichen uses a Grundfos MQ on-demand pump, eliminating the need for a pressure tank.
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WATER TREATMENT SYSTEMS
Preliminary filtration and a roof-wash system provide the first line of defense against contamination. Rainwater harvesting systems supplying potable water also should include measures to treat water before use. Several treatment options, including microfiltration, UV sterilization and ozonation, are available. Many experts agree that filtration and UV treatment provide adequate protection, making ozonation unnecessary.
Most systems use a combination of physical filters, which remove particulates, and a UV-light chamber, which kills bacteria and other organisms by exposing them to high-energy ultraviolet light.
Water treatment systems can add significantly to the initial cost as well as operating costs of a rainwater system. A UV sterilization system costs from $300 to $1,000 or more. Because the lamp generating the UV light needs to be left on all the time, annual electricity consumption can be significant. An ozonation system can cost more than $1,200 and can consume as much as 6,000 kilowatt-hours per year (primarily to operate a circulating pump that mixes the ozone in the cistern 12 hours per day).
A less expensive option is to treat water with chlorine or iodine, as is typically done with municipal water. The most common chemical added is chlorine in the form of sodium hypochlorite, which is available in liquid form. Household bleach, which is 5 percent sodium hypochlorite, is commonly used. The downsides to chlorination are the taste of the treated water and health concerns about harmful chemicals that could result from the added chlorine. In the presence of organic matter, chlorinated hydrocarbons, which are suspected carcinogens, may be formed.
OPERATION
"The privilege of [water] independence comes with responsibility," says Heinichen. "You are the sanitation engineer, the maintenance mechanic, the troubleshooting technician. You can't point the finger at some hapless bureaucrat if you let your pipes freeze or you forget to change your filters or you don't keep your gutters clean or can't learn to conserve during dry spells."
To keep a rainwater harvesting system functioning properly, periodic maintenance is required — this is particularly important with systems used for potable water. Gutters and downspouts need to be kept free of leaves and other detritus. Roof-wash water may need draining after each storm. The cistern may need periodic cleaning or repairs if cracks or leaks develop. Filters and LTV lamps need to be replaced on a regular schedule. Pumps and ozonation systems may need occasional servicing. All piping and connections should be inspected periodically. Finally, occasional testing should be considered to ensure that suitable water quality is being achieved.
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