Water may be polluted when pollutants come from point or non-point sources. Non-point sources include those sources that are non-discrete or that do not originate from one discrete source. Non-point pollution arises from the cumulative effect of contaminating agents in little quantities over a large area. When nitrogen compounds found in fertilizers, herbicides, pesticides and other agricultural products leach out, it can easily cause pollution. Sheet flow over land used for agriculture may lead to pollution of water as the nutrients that were present in soil runoff in storm water. Point sources of pollution are those sources that come from discrete sources. For example, when a manufacturing company discharges hot water from its cooling system into a river, lake or other water body making the water body to become warm, pollution occurs from a point source.
There are a wide range of agents that may cause water pollution. Some of these pollutants include pathogens, chemicals, and physical changes to the natural characteristics of water. While some minerals naturally occur in water, when their concentration in the water goes beyond the natural limit, the water is considered to be contaminated. Also, when substances that cause oxygen to be depleted in water such as man-made chemicals, grass and leaves, water pollution occurs.
Pathogens or disease causing organisms such as Salmonella, Giardia lamblia, Burkholderia pseudomallei, and Cryptosporidium parvum may get into the water when waster water or sewage is not adequately treated (Tennessee Department of Environment and Conservatio, 2002). Chemical contaminants of water may include detergents, petroleum hydrocarbons, volatile organic compounds (VOCs), products used for disinfection and waste from tree logging operations. Inorganic water pollutants include sulphur dioxide that is