For millennia, wells have provided people with access to plentiful water in areas where they otherwise would not be able to live. When a well runs dry, it can disrupt an entire community, making it impossible to sustain agriculture, industry and life itself.
Sometimes a well will start to "run dry" when there is nothing wrong with the actual aquifer providing water. The simplest cause for this is mechanical failure. The pump may be broken or clogged, there may be a fault with the electrical system or a leak in a pipe may be preventing the well water from reaching the house. Minerals can also build up inside the well, decreasing the quality and quantity of the water that flows.
Wells can only produce water at a certain speed. During periods of high use, the well may start to sputter or temporarily cease to produce water. Your well may stop producing sufficient well water when your family are all taking morning showers, for example. If your neighbor draws his water from the same source, it can compound the problem. A well that provides just enough water output for one family will be quite inadequate for two.
Sometimes, a well becomes truly exhausted. Wells work by accessing groundwater that flows down into underground rivers, called aquifers, over many years. If a community uses well water faster than the aquifers can be replenished by rainfall, the groundwater will be depleted, and the community will have to drill deeper and deeper wells.
Environmental and demographic shifts can also make an impact on the speeds at which wells run dry. Drought can put a heavier strain on groundwater stores. A local population increase can also strain aquifers, using up wells much more quickly than they otherwise would be used.