Well Volume Calculator

A drilled well is treated as a vertical cylinder, so the standing water it holds is the casing cross-section multiplied by the height of the water column, where that column equals total depth minus the static water level. Static water level is the depth from the surface to the water surface after the well has rested, conventionally at least 24 hours without pumping, so the aquifer has returned to equilibrium. Converting cubic feet to US gallons uses the factor 7.48052, which produces a convenient constant for each casing size: about 0.653 gallons per foot for 4-inch casing, 1.469 for 6-inch, and 2.611 for 8-inch. Six-inch casing dominates residential drilling in the United States because it accepts a standard 4-inch submersible pump with working clearance. Multiplying gallons per foot by the water column gives total volume in one step. The critical caveat is that standing volume is not water supply. Volume is a static snapshot, while yield, the rate at which the aquifer refills the bore, determines how long you can pump. A well with 220 gallons standing and a 5 gallon per minute recovery rate pumped at 10 gallons per minute draws down and eventually runs dry, which can damage the pump and, in unconsolidated formations, the bore itself. Yield is measured by a pump test rather than calculated, and 3 to 5 gallons per minute is the usual threshold considered adequate for a single-family home against an average US household demand of roughly 300 gallons per day. Geometry adds further error: many bedrock wells are cased only through the overburden and are open-hole below, so the actual diameter varies with depth. For shock chlorination the standard dose is 1 pint of unscented household bleach at 5.25 to 8.25 percent sodium hypochlorite per 100 gallons, held 12 to 24 hours, with coliform retesting 7 to 10 days after flushing.

Deep well drilling is ancient. Chinese well borers used percussion drilling with bamboo cable and iron bits to reach brine and natural gas at depths of several hundred metres by the Han period, a technique conceptually identical to the cable-tool rigs that mechanised American drilling in the nineteenth century. The term artesian comes from Artois in northern France, where wells drilled from the twelfth century onward tapped confined aquifers under enough pressure to flow at the surface without pumping. Rotary drilling displaced cable tool for most water well work in the early twentieth century, making 6-inch residential boreholes fast and cheap enough to become the default rural water source. The quantitative side arrived later. In 1935 Charles V. Theis of the United States Geological Survey published the non-equilibrium equation describing how water levels draw down around a pumped well over time, which turned well testing from rule of thumb into hydraulics and remains the basis of modern pump test analysis. The National Ground Water Association, founded in 1948, developed professional standards and driller reporting practices, and driller logs recording depth, casing size, and tested yield became the documents well owners rely on for exactly the inputs this calculation needs. The Safe Drinking Water Act of 1974 regulates public water systems but leaves private wells outside federal oversight, so casing, grouting, and sanitary seal requirements are set by state and local codes, and the EPA advises private well owners to test annually for coliform bacteria and nitrate on their own initiative.