Cisterns are used for the capture and storage of rainwater for later use in irrigation and household water supplies. Although not suitable for drinking unless purified, rain water is suitable for toilet and clothes washing purposes. A cistern can be made of any waterproof material.
Cistern sizes can range from hundreds of gallons to hundreds of thousands of gallons. They are used for residential and industrial or commercial properties. They can be above or below ground. They can be pre-made or commercially bought. They can also be home-made out of materials found around the home or at the hardware store.
The benefits of harvesting rainwater include the reduction in consumption of potable water. This will lessen the drain on the water supply. It will cut down on your water bill. It will also reduce run off volume to areas of compacted soil, high water levels and during peak flow times.
Components of a Cistern
Most cisterns have a cover to protect the water from evaporation and contaminants that are not already in the water. The cover also helps prevent the breeding of mosquitoes and the growth of algae. They should have a debris screen and tube filter, which block organic material from entering the cistern.
An inlet tube with a first flush diverter is used to eliminate the most dirty water from entering the cistern. Rainwater can contain many harmful contaminants. These range from bacteria from animal droppings, pesticides from agricultural use, lead from lead-containing painted surfaces, various heavy metals and general dirt and grime. There are numerous other possible contaminants and rainwater should never be used for human consumption without some kind of purification.
An access hatch should be incorporated into the well of the cistern for monitoring the water supply. Some kind of pump system should be employed. If you choose not to use a pump then you will have to rely on gravity for distribution of the water. If this is the case then consider placing the cistern at the highest point of your property.
An irrigation system with pipes and valves can be all you need to supply water to your yard or property. If you do use a pump then the irrigation system is unlimited in it’s direction of water flow.
A water level gauge, a drain for cleaning and a sediment trap are optional additional components that may or may not be included in the set up of your rainwater harvest system. Another possibility is the addition of extra storage tanks should your water needs increase.
The size of a cistern should be directly proportional to the size of the drainage areas that will feed into it. Another factor for determining size is the purpose that the water is going to be used for. You need to consider what uses and how much water is needed for each one.
A third thing to help determine the size of cistern needed is the length of the dry season. This is more important than the amount of rainwater able to be collected. This will determine how long the water supply will need to last. This is especially important for areas where there is no city water supply available.
In areas where the cistern will be exposed to cold weather for extended periods of time, you will need extra insulation on any area of the cistern that is exposed to the elements. If using an underground cistern, you may not be able to place it underneath the freezing depth but you can insulate it below the surface and above the top to prevent freezing. Water levels should be lowered at the beginning of winter in order to prevent damage or cracking of the tank from water freezing.
Semi-annual or annual inspection of all the parts of the cistern should be done. Check the catchment area for buildup of organic or other matter. Downspouts, screens and gutters should be checked for blockages and damage. Piping, tubing and plugs should be checked for leakage and cracking. They should be replaced as necessary.
Photo by Orin Zebest, Creative Commons Attribution License