Freshwater Generator
A Freshwater Generator (FWG) produces fresh water from seawater so a ship can be largely self-sufficient in water at sea. The common type is an evaporator that boils seawater under vacuum — so it evaporates at a low temperature — using waste heat from the main-engine jacket cooling water, then condenses the vapour into fresh distillate. Reverse-osmosis units are also used.
The water produced supplies the boilers, the engine systems, and, after treatment, domestic and drinking use. Making water from waste heat is nearly free, so the freshwater generator saves the cost and logistics of carrying or bunkering fresh water.
Carrying all the fresh water a ship needs for a long voyage would take up valuable weight and space; making it on board from waste engine heat is almost free and self-sufficient. The freshwater generator is a quiet efficiency win that keeps the ship independent of shore water supplies.
How does a freshwater generator make water from seawater?
Most use an evaporator: seawater is boiled under vacuum at a low temperature using waste heat from the engine cooling water, and the vapour is condensed into fresh distilled water. Some ships use reverse-osmosis membranes instead.