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The availability of clean water is paramount to the sustainability of life and good health. Adequate supplies of water are essential for agriculture and societal development. Water availability is scarce, with less than 1% of global fresh water accessible while the global demand for water is increasing substantially. By 2050, feeding a planet of 9 billion people will require an estimated 50% increase in agricultural production and a 15% increase in water consumption.

The United Nations reports that billions drink polluted water that could be harmful to their health. Unsafe polluted water kills more people each year than war and all other forms of violence combined. Almost 80% of diseases in developing countries are associated with water, causing some three million early deaths. The World Health Organization (WHO) and many countries have established regulations and guidelines to protect water.

Factors impacting the global availability of water include climate change, and the contamination of water from biological agents, chemicals, and a wide range of substances that are detrimental to human, plant and/or animal life. These contaminants include fertilizers and pesticides from agricultural runoff; sewage, and food processing waste; plastic; chemical wastes from industrial discharges; chemical contamination from hazardous waste sites; and lead, mercury, and other heavy metals.

The earth’s water is constantly in a cycle of evaporation and precipitation (Figure 51–1). Once deposited on the earth’s surface, water may run off, be impounded, or percolate through various layers of soil, sand, and rock to become free-flowing water or confined water. Deep aquifers often are confined. Therefore, they do not participate in the evaporation and precipitation cycle unless the confining zone above them has been penetrated and fluids extracted. Evaporation from saline water sources, the oceans, and large salt marshes also contributes to the total airborne water vapor that eventually may precipitate to the earth’s surface. The process of evaporation and precipitation has the potential to cleanse water of organic and inorganic contaminants, as does percolation of water through sand and soil and the action of soil microorganisms.

Climate change negatively impacts the water cycle by reducing the availability of drinking water. Precipitation in a warming world will not be uniform. In dry subtropical regions there is projected to be a reduction in mean precipitation crucially reducing renewable surface water and groundwater resources. While in mid-latitude land masses and wet tropical regions there is projected to be an increase in the intensity and frequency of precipitation. The interaction of increased temperature; increased sediment, nutrient and pollutant loadings from heavy rainfall; increased concentrations of pollutants during droughts; and disruption of treatment facilities during floods will significantly reduce drinking water quality and availability.


Water usage is based on geographic location, population density, and ...

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