We tend to think of water in terms of a particular purpose: is the quality of the water good enough for the use we want to make of it? Water is fit for our own use but may be unfit for another's. We may, for instance, trust the quality of lake water enough to swim in it, but not enough to drink it. Along the same lines, drinking water can be used for irrigation, but water used for irrigation may not meet drinking water standards. It is the quality of the water, which determines its uses.
             There are many causes for water pollution but two general categories exist: direct and indirect contaminant sources.
             Direct sources include sewage outfalls from factories, refineries, waste treatment plants etc. that emit fluids of varying quality directly into urban water supplies. In the United States and other countries, these practices are regulated, although this doesn't mean that pollutants can't be found in these waters.
             Indirect sources include contaminants that enter the water supply from soils/groundwater systems and from the atmosphere by means of rainwater. Soils and ground waters contain the remains of human agricultural practices (fertilizers, pesticides, etc.) and improperly disposed of industrial wastes. Atmospheric contaminants are also resulting from human practices (such as gaseous emissions from automobiles, factories and even bakeries.
             Contaminants can be broadly classified into organic, inorganic, radioactive and acid/base. Examples from each class and their potential sources are too numerous to discuss in great detail in this paper.
             The effects of water pollution are varied. They include poisonous drinking water, poisonous food animals (due to these organisms having bioaccumulated toxins from the environment over their life spans), unbalanced river and lake ecosystems that can no longer support full biological diversity, deforestation from acid rain, and many other effects. These effects are, of course, specific ...