Cost issues   Although purchasing a cistern or rain barrel can initially be expensive, it will eventually pay for itself many times over in saved water costs. The most expensive part of a rainwater harvesting system is the cistern itself. The cost of constructing cisterns can vary greatly depending upon their size, material, and location. The cost goes up dramatically when the cistern is installed by a contractor. The degree of water treatment necessary also affects the cost, as does capacity. Water tanks with a capacity of 2000 gallons or less cost between $0.45 and $1.00 per gallon of storage, and concrete tanks are more expensive than equivalent synthetic tanks. Larger-volume concrete tanks cost roughly $1.25 per gallon of storage. Another major expense when installing a cistern is the concrete work. Sizes of cisterns can vary from hundreds of gallons for residential use to tens of thousands of gallons for commercial and/or industrial uses. Costs may increase if the cistern is to be placed below ground and excavation is required.     http://www.lid-stormwater.net/raincist/raincist_cost.htm