Cisterns are the champions of rain water harvesting. They have two purposes, 1) collect and store rain water to be used for irrigation (yard watering) purposes later (hello water bill savings!), and 2) to stop roof water runoff from carrying pollutants into watershed areas. Cisterns come in two forms, underground or above ground. Due to the volume of how much water they can store AND if you are putting in an underground cistern, they can sometimes require a type of permitting from the city.
