In the grocery store we are often asked “paper or plastic?” We have a choice based on convenience and our perception of recycling benefits. However, the selection of casing for a water well is not something that can be left to consumer choice. The professionals responsible for the design and construction of a well make their decisions to use steel or plastic based on practical installation criteria, the type of equipment they will be using to construct the well, state and local code requirements and perhaps also on cost. The purpose of a well is to provide access to the aquifer. Once constructed, the well is the conduit for the pumping system that will bring water from the aquifer for use at the surface.
Casing provides support for the wall of the well so that loose rock fragments or unconsolidated sand and gravel through which the well has penetrated do not collapse into the well shaft. The casing protects the electrical wires, pull cable and water tubing/piping that are connected to the submersible pump. It also provides a vertical-cylindrical surface that in conjunction with the outer vertical wall of the drilled hole can facilitate the placement of an impermeable grout seal around the well casing. The grout seal in the annular space outside of the casing prevents surface water and potential contaminants (bacteria, fertilizers, pesticides etc.) from descending along the outside wall of the well down to the zones of stored ground water.