The cistern inlet and outlet should be designed to minimize stirring the solids settled on the tank bottom, and the tank should include a manhole, a vent, a cleanout sump and an overflow pipe. If the cistern is to store potable water, a vertical fill pipe for use by water haulers is also desirable. Consult the listed references for design details. Except on steeply sloping sites, a pressurized system is needed to distribute the water from the cistern. The outlet line from the cistern should be buried beneath the frost line.
Rainwater is naturally acidic, and corrosive to metal tanks and household plumbing.
In homes where the water lines are copper, joined with lead-containing solder, the rainwater should be neutralized before it enters the water lines to prevent mobilizing lead and copper into drinking water. Sacks of crushed limestone used to anchor the inlet pipe in the cistern serve the same purpose. The design of an individual rainwater harvesting system depends on the planned water use, the layout of the yard or farmstead, and the reliability of the water supply that is needed. Different approaches are taken in different parts of the country. Roughly 35 percent of the precipitation that falls on a Montana roof is unavailable for use because of evaporation, leakage or diversion by the roof washer.