Water is a crucial question  everywhere even on a ship !!

aboard the water tanks hold 150 Tons ( 150000 L): that is to say 3 day supply !

So the ship has to produce fresh water very soon after the departure.

The production is about 50 tons of fresh water a day; about 575 L /pers/day ( average consumption in USA : 400-500L /pers/day).

How to  produce fresh water?

By desalination: using sea water, removing salt.

2 processes are used after the sea water has been pumped into a tank through a steel mesh and a 30 micron filter.

First process:

• The water is poured out in an other tank under low pressure where the water can boil at 165°F ( instead of 212°F at standard atm. pressure. 165°F = +/_ 73,9°C).
• Water vapor is collected
• condensed
• stored in a tank.Second process: longer with a lot of steps:
  • the incoming sea water passes through heat exchanger
  • then through a sprayer  and
  • the vapor passes through a demister and a condenser
  • the liquid water under high pressure and temperature passes in coils
  • the vapor is cooling through a heat exchanger ( exchange with the incoming sea water )
  • the water is finally collected in a holding tank.

  At different levels of these processes the water is treated by chemicals as bromine and chlorine .

  When needed, water from holding tank passes through a pressurized tank and just before passing into the pipes for consumption water is sterilized by UV light