An aquifer receives 20 m3 of precipitation and loses 2 m3 of water through natural movement. If the water budget must be balanced, how much water can be pumped from the aquifer?

A balanced water budget means water entering equals water leaving. The aquifer gains 20 m³ from precipitation and loses 2 m³ through natural movement, leaving 20 − 2 = 18 m³ available to pump. The correct choice is 18 m³.

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