Each ship is mounted with fresh water production unit thatproduces fresh water directly from sea water. The efficient fresh water production part of the ship assist the vessel manager to save a great deal on additional fresh water expenses incurred by buying fresh water from port sellers.

What are popular techniques for producing fresh water on ships:

  1. Fresh water producing generator
  2. The Reverse osmosis process.

The reverse osmosis process is one of the present methods used by the shipping industry to generate fresh water from sea water. This type of water production does not make use waste heat source, not like fresh water generator, to desalinate the sea water to convert it into fresh water with a low salt ppm.

What is the principle of Reverse Osmosis

As the name indicates this methods works on reversing the osmosis principle.

When the chemical solution is taken from pure water by a semi permeable membrane (letting the passage of water not salt) then the pure water passes through the membrane till all the pure water has gone through or until the hydrostatic pressure head of the salt solution is greatly big enough to arrest or stop the process.

Reverse osmosis is the method of using this phenomenon in reverse direction. This leads to water being forced through the membrane from the concentrated solution toward the more dilute one. This is made possible by putting pressure of the osmotic pressure of the concentrated solution.


The osmotic pressure of sea water is 28 bars but to override system losses and the fact that the sea water concentration increases as it passes via the length of the membrane, much higher pressure around 40-70 bar, depending upon the plant size, is needed

A triplex plunger pump is frequently used to produce high pressure across the membrane. The membrane that is used has a very fine barrier of dense holes which only lets water and gases to pass through, while stopping the passage of solutes the likes of salt and other impurities.

The fresh water that is produced after this very stage is treated with chemicals and other ultraviolet treatment to makes it drinkable and useful for other domestic purposes.