The quality of any body of surface or ground water is a function of either both natural influences and human influences. Without human influences water quality would be determined by the weathering of bedrock minerals, by the atmospheric processes of evaporation, transpiration and the deposition of dust and salt by wind, by the natural leaching of organic matter and nutrients from soil, by hydrological factors that lead to runoff, and by biological processes within the aquatic environment that can alter the physical and chemical composition of water. Declining water quality has become a global issue of concern as human populations griesrow, industrial and agricultural activities expand, and climate change threatens to cause major alterations to the hydrological cycle.