Because the process for desalination is the exact opposite, it?s called reverse osmosis, or just RO. A pre-treatment step is required before RO to provide high quality water and reduce membrane fouling. The most common pre-treatment steps include coagulation and filtration or microfiltration.uick OutlineDesalination is a practical way of making salty water drinkable and it is used widely around the world now, especially in very dry countries and on ships and small islands. The process is quite expensive and it uses a lot of energy.