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WHAT IS PURE WATER?
We know that all life is dependent on water and that water exists in nature in many forms like clouds, rain, snow, ice, and fog; however, strictly speaking, chemically pure water does not exist for any appreciable length of time in nature. Even while falling as rain, water picks up small amounts of gases, ions, dust, and particulate matter from the atmosphere. Then, as it flows over or through the surface layers of the earth, it dissolves and carries with it some of almost everything it touches, including that which is dumped into it by man.

These added substances may be arbitrarily classified as biological, chemical (both inorganic and organic), physical, and radiological impurities. They include industrial and commercial solvents, metal and acid salts, sediments, pesticides, herbicides, plant nutrients, radioactive materials, road salts, decaying animal and vegetable matter, and living micro organisms, such as algae, bacteria, and viruses. These impurities may give water a bad taste, colour, odour, or cloudy appearance (turbidity), and cause hardness, corrosiveness, staining, or frothing. They may damage growing plants and transmit disease. Many of these impurities are removed or rendered harmless, however, in municipal drinking water treatment plants.

Pure water means different things to different people. Homeowners are primarily concerned with domestic water problems related to colour, odour, taste, and safety to family health, as well as the cost of soap, detergents, "softening," or other treatments required for improving the water quality. Chemists and engineers working for industry are concerned with the purity of water as it relates to scale deposition and pipe corrosion. Regulatory agencies are concerned with setting standards to protect public health. Farmers are interested in the effects of irrigation waters on the chemical, physical, and osmotic properties of soils, particularly as they influence crop production; hence, they are concerned with the water's total mineral content, proportion of sodium, or content of ions "toxic" to plant growth.