Hydrologic impacts of mining activities include any which change the quantity, quality or natural cycling of water resources. Since the water cycle on Earth is closely linked to the terrestrial, subterranean and atmospheric environment, there is much potential for disruption of the "hydrologic balance."

Examples of possible hydrologic impacts from mining include:

• Water table draw-down. This is when mine dewatering or other pumping (i.e., for water usage) at a mine site causes a depression in the natural subsurface water table.
• Alteration of surface flows. This is when changes to the contour of the land change the natural flow of surface waters. For instance, valley filling can change stream flows; changes to soil compaction can also change percolation rates of water, which may alter peak flows and flooding during storm events.
• Alteration to water quality. This is when sediment, silt or leached constituents enter surface or groundwater resources. Deforestation can lead to increased erosion and sediment transport during the mining process; acid mine drainage can impact surface waters; and underground injection of wastes might cause contamination of groundwater aquifers.