Well

A well is a hole drilled, dug, driven or bored into an aquifer, the layer of rock or gravel that holds water underground. Lifting it to the surface gives a supply that owes nothing to recent weather. That is what carries a design through a drought that has emptied every tank. Finding water is not guaranteed: in hard rock fewer than half the holes drilled may strike a useful supply, so the cost includes the dry ones. In most places drilling is licensed work.

A well delivers nothing on its own. Behind it sit a pump, a power supply, a storage or pressure vessel and some treatment, and the design question is yield rather than depth. A system has to meet peak demand for at least two hours, and a well that cannot keep up is fixed with a storage tank rather than a bigger pump, at roughly 380 litres (100 gallons) per person in the house. A pressure tank is no substitute: only about a fifth of its volume is usable water. The pump is where the dependency sits, so a windmill or an animal-drawn lift removes the need for electricity.

Contamination usually enters at the wellhead, not the aquifer. One survey of private wells found 70 percent with unsanitary caps and 40 percent failing a health standard, which is why a gasketed cap and a setback of at least 30 m (100 ft) uphill of any septic field or barnyard matter. Grout around the casing is nearly impossible to correct later, so it is settled on drilling day. The slow failures follow. Iron bacteria clog the screen, minerals encrust it, and corrosion widens its openings until the well pumps sand, the leading cause of pump failure. A drop of a quarter in yield signals that rehabilitation is due, and drought shows up as equipment failure when a falling water table leaves a submersible pump running dry. Upkeep is an annual bacteria test and a regular look at the cap, but the maintenance burden belongs to the pump, not the hole.