Collecting for Household Use
Things get more complicated if you're planning to drink, wash, or bathe with rainwater. You need specific types of roofs, gutters, and storage tanks, as well as a way to filter and purify the water and pump it into your house.
Filter can take out most bacteria and particulates, and reverse osmosis will catch the sulfuric and nitric acids in acid rain.
Unfortunately, there are areas with such heavy air pollution that rainwater cannot be filtered enough to make it drinkable.
"If you live in a highly industrialized area, I recommend using rain for gardening only," cautions Hoffman. "If you have any concern about rain quality, have a professional water test done on a sample."
Unpainted galvanized metal roofing is the best catchment surface for potable–water systems because it's smooth and nontoxic. Clay or concrete tile and slate also work well. Asphalt, asbestos, chemically treated wood shingles, and some painted metal roofs, however, can leach toxic materials and are recommended only for nonpotable water uses.
As in a simple system, gutters and downspouts should have leaf screens. But it's important that those gutters not have lead solder or lead–based paints. Seamless aluminum and vinyl gutters are fine. Also, a roof washer, a filtration system that removes any remaining leaves, debris, and bird droppings, should be placed in the line before the water enters
a storage tank.
Like nonpotable systems, storage tanks can be made of stone, cement, metal, wood, or fiberglass. But if you're planning on showering with or drinking rainwater, stone and cement can leach minerals, and galvanized tanks can release zinc in the water unless a PVC liner is used (zinc from galvanized roofs is filtered out before being stored).
Fiberglass tanks, though hardly the most attractive, are easily the cleanest and most durable. You'll need to keep the tank out of the sun in order to avoid algae growth. Tanks are sometimes buried, either partially or fully, to keep the water cool or to hide the tanks (and to prevent the water inside from freezing).
However, buried tanks add costs for excavating and can't easily be cleaned. A better option is to shade the tanks to ensure that only rain—and not sunlight—gets in.
By looking at the average rainfall levels in your area, you can figure out how much rainwater you can expect to collect per year and whether that will meet your family's water needs.
(An average household with newer plumbing fixtures such as 1.6–gallon–per–flush toilets and 2.5–gallon–per–minute showerheads uses roughly 55 gallons per person per day.)
In general, 1,000 square feet of roof will collect 600 gallons of water for every inch of rain that falls. Remember that actual rainfall amounts fluctuate with the seasons, while household needs remain reasonably steady.
If you're depending on rainwater for all or most of your water needs, your tanks have to be big enough to get you through the dry spells. Plus, you'll need a fair amount of space to house those tanks. Be sure to follow municipal restrictions on tank placement.
The cost of a 10,000–gallon tank, PVC lines to and from the house, all filters, UV light, pressure tank, and pump runs $7,500 to $9,000.
To entice more participants (and thereby relieve overburdened water service, Austin, Portland, Oregon, and other cities are offering incentives like tax–free equipment or property–tax rebates to install collection systems.
