Water pollution is a global problem and one that does not respect national boundaries. Sources of pollution may be domestic, agricultural or industrial. In less-developed countries, human and animal waste and sediments from unsound agricultural and forestry practices are the main pollutants. In more-developed countries; industrial pollutants, such as toxic metals, organic Chemicals and heat add to the water pollution problem. The effectiveness of treating wastes prior to their release into the environment determines the balance between potential and actual pollution.