Although all water that enters pit workings originates from atmospheric precipitation, the miner distinguishes between surface water and groundwater. Surface water enters the pit through openings in the mine at the surface of the ground, such as tunnel portals or shaft entrances. During heavy rain, water seeps into the earth and forms ground water when it meets layers of impervious rock. Pit water is mainly interstitial water and groundwater that seeps into the mine workings.