Shipboard potable water (drinking, bathing, whirlpools, etc.) either comes from a shoreside water treatment plant or is generated on board from seawater via Reverse Osmosis systems or Evaporators. Swimming pool water is typically seawater.

Shower water on a modern cruise ship is primarily produced through a high-fidelity process of desalination of seawater. The ship utilizes two main technologies: Reverse Osmosis (RO), which forces seawater through fine membranes to remove salt and impurities, and Evaporators, which use heat from the ship's engines to boil seawater and condense the steam into pure, distilled water. Approximately 90% of the fresh water used onboard is created this way, while the remaining 10% is "bunkered" (sourced from port municipal supplies) in large storage tanks. Once produced, the water is mineralized for taste and treated with UV light or chlorine to meet strict "High-Fidelity" USPH (U.S. Public Health) standards. After you use it in the shower, the "Gray Water" is sent to an Advanced Wastewater Purification (AWP) system, where it is treated to a level of purity higher than most land-based municipal systems before being safely discharged or reused for technical purposes like laundry or deck washing.