Urbanization and road building block movement of water into the soil and thus block recharging of aquifers.
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.