Pollution can make an aquifer unfit. Nearly half of all water used in the US comes from groundwater. In many areas of the US, aquifers are being used faster than natural recharge can replace. All are covered with water at least part of the year and have characteristic soil and plant associations. A watershed is all the land drained by a stream or river.
Water is one of the most important natural resources on earth.
We treat it as plentiful, inexhaustible with no intrinsic value. The amount of available freshwater is declining due to rising populations expressed through increased energy needs, increased irrigation and farming of marginal lands and increasing pollution. Africa, Middle East are the most water-poor regions. Irrigation tends to be very inefficient and excess water can be contaminated with fertilizer, pesticides or cause erosion. Developed nations use water in energy production.