One way to keep a record of the water levels in a well is to place a float at the end of a wire and lower it into a well. The float will go up and down as the water in the well goes up and down. The other end of the wire is attached to a machine that has a pen-like instrument attached, and the pen point moves up and down according to the action of the float. A roll of paper slowly rolls past the pen, so a record of water level is plotted continuously on the paper. Water levels in wells are constantly changing both in the short term and over the long term.
Some wells even have a seasonal change.
In the short term, water levels can be lowered just by pumping water out of the well for use. Also, a well may be pumped so much as to cause the water level in nearby wells to be lowered, too. In some places people have withdrawn water faster than water replenishes the aquifer, and the wells have stopped producing water. Sometimes this is a long-term problem occurring over a very large area. If it takes a long time to replenish the aquifer, maybe because the aquifer is composed of rock that only allows water to move through it very slowly, a field of wells may stop producing.