Posted: March 24, 2015
Use of rainwater cisterns may be increasing. Those living in areas where groundwater is scarce or unusable have to find other sources of water. Rainwater collection for household use is employed in areas that lack other good sources of water, such as the strip-mining region of western Pennsylvania.
Cisterns may also supply water to farms to fill watering troughs and rain barrels using water collected from barn and other out-building roofs. A storage cistern could serve as an emergency source of water for firefighting in case a pond was not nearby.
However, using rainwater for domestic water needs is not without its problems.
Water quality is a concern because rainwater and atmospheric dust collected on the roof contains contaminants which may pose a health threat to consumers. Lead and other pollutants may accumulate in cistern bottom sediments; and untreated rainwater is corrosive to plumbing systems. Rainwater cisterns can provide enough good quality water with proper planning and construction steps, and periodic maintenance performed on the cistern.
Cistern design should take several factors into account:
- Amount of rainfall available for use
- Roof area available for collecting that rainfall
- Daily water requirements of the household
All but the first of these factors can be controlled to some extent by the cistern owner.
Annual rainfall in Pennsylvania averages around 40 inches, ranging from as little as 30 inches, in drought years to 50 or more inches in wet years. Designing a cistern based on 30 inches should provide enough storage to get you through even the driest years.
It is important when designing a cistern system to have some idea how much water you will require from it every day. Common household planning provides for 50 to 75 gallons a day per person. A minimum storage capacity of 5000 gallons is recommended for domestic cisterns. Remember these words of wisdom when designing your cistern: "You pay for a large cistern once and a small one forever…"
Installing water-saving devices could considerably reduce household water use with no conscious effort by the family members. Information on water conservation in the home is available from your county extension office or view, Saving Money with Home Water Conservation Devices.
Locate cisterns close to the house or wherever the water is to be used. They may be built above or below ground, but below-ground cisterns are recommended certain parts of the country to avoid freezing during the winter months. Underground cisterns also provide relatively cool water even during the warmest months of the year.
Cisterns should be located where the area can be graded to provide good drainage of surface water away from the cistern, and low areas subject to flooding to should be avoided to reduce the chance of storm runoff contaminating the stored water. Locate cisterns upslope from any sewage disposal facilities; at least 50 feet away from sewer lines, septic tanks and absorption fields, and animal stables, and at least 100 feet away from cesspools and privies.
The choice of roofing materials use as collection surfaces for rainwater cisterns is important.
Cisterns can be constructed from a variety of materials including cast-in-place reinforced concrete, cinder-block and concrete, brick or stone set with mortar and plastered with cement on the inside, ready-made steel tanks, precast concrete tanks, redwood tanks, and fiberglass.
Roof washers and roof-water filters are also important construction features that will help insure good quality cistern water. Dirt and dust collects on the roof between rainstorms. Debris includes particles of lead and other atmospheric pollutants as well as bird droppings that enter the cistern along with the roof water. The use of roof washers and roof-water filters can reduce the amount of contaminants entering the system. Gutter guards should also be installed to keep leaves, twigs, and animals out but let water in.
Periodic cleaning of the cistern to remove the sediment accumulation is recommended every three to five years.
Water treatment will be necessary to insure safe, potable cistern water. Rainwater is acidic and therefore corrosive and will corrode household distribution systems unless neutralized, adding toxic metals such as lead and cadmium to the water. One simple thing you should do before using the tapwater for drinking or cooking is to allow the cold water to run for about a minute. This flushes the "stale" water (laden with toxic metals if from lead-soldered copper or other metallic pipe) from the supply line, especially after a tap has gone unused for several hours, or overnight. Rather than just letting the water run down the drain, use it for purposes other than drinking or cooking.
For complete information visit: Rainwater Cisterns: Design, construction, and water treatment