Reverse osmosis process for water purification does not require thermal energy. It makes water purifiers based on the process of reverse osmosis purification. Water purification is to be supplied by distillation and reverse osmosis. Perth began operating a reverse osmosis seawater desalination plant in 2006. Salt is difficult to remove except by reverse osmosis or distillation. Graphite oxides were studied for desalination of water using reverse osmosis beginning in the 1960s. Reverse osmosis (R/O) desalination units supplement rainwater harvesting on Funafuti. Two main processes are used, reverse osmosis or distillation. The treatment plant captures water from brackish streams which is desalinated using reverse osmosis. Government-installed reverse osmosis plants supply free filtered water. Fresh water is produced by either an evaporator or a reverse osmosis unit. Saltwater fish tend to lose water because of osmosis. Both processes rely on osmosis with membranes. The polymers are promising membranes for use in reverse osmosis. Many aquatic shops sell containers of reverse osmosis water for this purpose.