Pollution: Irrigation water can carry toxic pesticides and fertilizers from agricultural fields and bring these substances into the ground. Water from landfills does the same. Underground storage tanks containing gasoline may also leak and get into groundwater. Rocks and minerals are able to filter out some pollutants but not all. If a pollutant enters an aquifer, contamination spreads out inch by inch and continues in the direction the water is moving in.
Groundwater overuse for agriculture leads to saltwater intrusion and subsidence. Subsidence can occur beneath structures and can cause property destruction. Saltwater intrusion is when salt water enters the aquifer, making groundwater less useful for irrigation and drinking.