Article: What influences the quality of ground water? "Pure" water does not exist. All natural water contains some dissolved gases and minerals. Ground water quality is influenced by the chemical make-up of the geologic formations in which it occurs, and the length of time that it has been underground.(Water Conditioning)

Overall, ground water is cleaner and purer than surface water. Most ground water moves very slowly, and its long travel time in a dark, cool environment means that it has few, if any, of the millions of microorganisms that virtually always are found in lakes or rivers. Ground water usually is free of sediment and constant in temperature. In addition, ground water naturally is protected underground and less likely to become polluted than surface water. However, ground water may be more mineralized than surface water because its slow movement gives time for it to dissolve minerals from the rocks it touches, allowing it to pick up various rock-related chemical constituents.

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