Drilled well tapping waterbearing sand. General design Two general types of wells are commonly used for private water supplies in Iowa. They are usually less than 100 feet deep and often tap waterbearing sands that yield 5 gallons per minute or less. The large-diameter casing serves as an underground reservoir, storing approximately 50 gallons of water in each lineal foot of casing filled. During peak water-use periods of the day, water is pumped out of storage as needed.
Seepage refills the well during periods of low water use.
They are used throughout Iowa at depths ranging from 20 feet to more than 3,000 feet. Little water is stored in the small-diameter casing so the pumping rate is limited by the yield capacity of the waterbearing formation. Above-ground storage must be used to meet demands that exceed the well capacity. Although bored wells have typically been considered more prone to contamination than drilled wells, both types can be adequately protected if the protective features described in the following paragraphs are applied. All wells should have at least 20 feet of permanently installed casing.