How Cruise Ships Make Fresh Water

Modern cruise ships have an insatiable thirst for fresh water. Some of today's biggest cruise ships, like the Grand Princess, use more than 260,000 gallons of fresh water every day. Rather than carry all this water from the embarkation port, or rely on local ports of call, the newest state-of-the-art cruise ships transform salty sea water into fresh drinking water by a process known as desalination.

The desalination process on a cruise ship uses either flash evaporators or osmosis. Flash evaporators boil sea water and re-condense the steam vapor, producing fresh drinking water. This method is similar to the natural water cycle, where sea water is heated by the sun, rises as steam to form clouds, and then falls back to earth as rain. The second method, osmosis, filters sea water through a fine membrane to separate pure water from salt and other minerals. Cruise ships do not desalinate water near ports or close to land, because coastal waters are the most contaminated.

After desalination, the water is passed through a mineralization plant, which adds minerals. This is necessary because the healthy minerals naturally found in drinking water have been removed by desalination. At this stage, the water is also checked for impurities, sanitized, and the pH is corrected. The water is then sent to massive storage tanks on board the cruise ship. On the Grand Princess, for example, these storage tanks hold up to 500,000 gallons of fresh water.

Next, the water is routed to hot and cold systems. Miles of distribution pipe move the water around the cruise ship.

After the water is delivered through a sink or shower, and used by cruise ship passengers or crew, it must be treated again before it can be discharged. All cruise ships must follow strict environmental laws in the treatment of waste water. Even after treatment, the water is not immediately released, but is held in special storage tanks when the ship is close to land, in port, or other sensitive environments.

It's a complex process, but necessary in order to ensure the health of cruise ship passengers and the natural environment.

Something to think about next time you choose a cruise.

Recommended reading:
Complete Guide to Cruising & Cruise Ships 2010