Water purification involves the elimination of chemicals, biological contaminants, suspended solids and gases from contaminated water. For water purification, a number of processes are used such as boiling, distillation, reverse osmosis, desalination, in situ chemical oxidation, UV light and ozonation. There are a number of companies that offer water purification equipment for both residential and commercial applications. Examples of the equipment include reverse osmosis and drinking water systems, filtering systems, alkaline drinking water systems, and UV sterilizers. Some of the aspects that should be considered while buying water purification equipment are: durability, availability of spare parts, pricing and after-sales service.