Water quality is one of the most important aspects of fish keeping, production, and health. The health of a fish is directly related to the quality of its aquatic environment. Failure to provide timely intervention and correction of poor environmental conditions can result in catastrophic losses, which can have devastating financial and/or emotional effects on the owner of the fish. Some aquarists and commercial fish facilities have access to water from streams, rivers, ponds, reservoirs, lakes, bays or oceans. Water quality for these sources can vary greatly depending on location, human usage, and environmental factors, and in some cases, there may be legal issues associated with its use. Though some generalizations can be made, ground water can vary greatly from location to location. Reverse osmosis is a method by which water is forced through a semipermeable membrane to remove many of the impurities from the water.