When the withdrawal of ground water in an aquifer exceeds the recharge rate over a period of time, the aquifer is overwithdrawal. There are two possible effects from the overwithdrawal of water from an aquifer.

First, when the amount of fresh water being pumped out of an aquifer in a coastal area can not be replaced as fast as it is being withdrawn, salt water migrates towards the point of withdrawal. This movement of salt water into zones previously occupied by fresh water is called salt water intrusion. Salt water intrusion can also occur in inland areas where briney water underlies fresh water.

Secondly, in some areas overwithdrawal can make the ground sink because ground water pressure helps to support the weight of the land. This is called subsidence. Sinkholes are an example of this effect.

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