Hi,
I second what dscasseta said, fresh water is used everywhere on the ship.
*******************************************Useless, "out of interest" information incoming!***************************************************************
The water used is from whats called "technical water" tanks. It is the same water which is used by the high pressure cleaners on deck.
The water is either made by filtration or evaporation. Filtration is done by reverse osmosis, ie very fine filters that only water molecules can pass through. The other method, which is used when the ship is underway, is using an evaporator, this uses the waste heat from the engines to boil off water within a vacuum.
The water produced by both methods is then treated and stored for use.
Each of the Dream class vessels have two of each, for redundancy.
**************************************************End of useless information***********************************************************************