Reverse Osmosis is the process that makes desalination (removing salt from seawater) possible. In this process, water is taken out from the sea and first treated to remove impurities such as oil, seaweed, algae etc. and produces potable water. Once the saltwater is free of organic substances, it is subjected to reverse osmosis. After water is passed through membrane system, we get two streams: one is permeate and another is reject. This plant generally runs at a lower recovery. Existing desalination technology requires a substantial amount of energy, usually in the form of fossil fuels, and so the process is expensive. For this reason it is generally used only where sources of fresh water are not economically available.