Cruise ship tap water is generally safe to drink. Major cruise lines produce their own freshwater from seawater using industrial filtration systems, and ships sailing from U.S. ports are subject to inspections by the CDC’s Vessel Sanitation Program. That said, the water goes through a very different journey than what comes out of your tap at home, and understanding how it’s produced and maintained can help you decide whether to drink it or stick to bottled water on your next voyage.
How Cruise Ships Make Freshwater
Most modern cruise ships produce the majority of their drinking water onboard by converting seawater through one of two main methods: reverse osmosis or thermal distillation.
Reverse osmosis forces seawater through a semi-permeable membrane under high pressure. Water molecules pass through, while salt, bacteria, and other impurities get left behind. The result is extremely pure water, often purer than municipal tap water. The downside is that the process strips out healthy minerals and lowers the pH, so ships typically add minerals back in and rebalance the water before sending it to your cabin.
Thermal distillation is the older method. Seawater is heated until it evaporates, leaving the salt behind, and then the steam is condensed back into liquid freshwater. Many ships use waste heat from the engines to power this process. One important detail: when evaporation happens below 80°C, the World Health Organization notes there’s no guarantee the water is free from pathogens, so it requires disinfection before it can be classified as potable.
Ships can also take on water from port municipal supplies, a process called bunkering. The WHO recommends that bunkered water meet its drinking water quality guidelines or relevant national standards, whichever are stricter. Port water is monitored for bacteria like E. coli, disinfectant levels, turbidity, and corrosion-related contaminants before it’s loaded aboard.
How the Water Is Monitored Onboard
Once water is produced or loaded, it’s stored in large holding tanks and distributed through miles of internal plumbing. Cruise lines are required to maintain a detectable disinfectant residual (typically chlorine or a similar agent) throughout the distribution system to prevent bacterial growth during storage and transit through pipes.
The CDC’s Vessel Sanitation Program sets environmental public health standards that inspectors use during unannounced ship inspections. These standards, updated for 2025, cover water system design, maintenance, and sanitation. Ships operating out of U.S. ports are also expected to develop and implement a comprehensive water management program covering every system and device that uses water onboard, from galley sinks to cabin showers to spa pools.
You can look up any ship’s most recent VSP inspection score on the CDC’s website. Scores of 86 or above out of 100 are considered passing, and most major cruise lines consistently score in the high 90s.
The Legionella Risk in Ship Plumbing
One specific concern with cruise ship water isn’t about drinking it but about breathing it in. Legionella bacteria can grow in warm, stagnant water inside plumbing systems and become dangerous when inhaled as fine mist from showers or hot tubs. This causes Legionnaires’ disease, a serious form of pneumonia.
The CDC requires cruise ships to follow industry standards for Legionella prevention. This includes flushing the entire potable water system, tanks, and all associated components before resuming operations after any period of reduced use. Hot and cold water must be flushed through every point of use on the ship, including cabin showers and faucets, galley areas, recreational spaces, and salons. Hot water lines need to reach their maximum temperature during flushing, since Legionella thrives in warm water between roughly 77°F and 113°F but dies at higher temperatures.
Ships that pursue routine environmental Legionella testing are directed to use accredited laboratories. This matters most after a ship has been idle or operating at reduced capacity, when stagnant water in pipes creates ideal conditions for bacterial growth.
Why It Might Taste Different
Even when cruise ship water is perfectly safe, many passengers notice it tastes flat or slightly off compared to what they’re used to at home. This is largely because reverse osmosis strips nearly everything from the water before minerals are added back. The remineralization process restores safety and basic mineral content, but it doesn’t replicate the exact mineral profile of your home tap water. Storage in large onboard tanks can also contribute a faint taste, particularly toward the end of a long voyage.
The pipes themselves play a role too. Cruise ships have extensive plumbing networks, and water sitting in lines between uses can pick up trace flavors from the piping material. This is a cosmetic issue rather than a safety one, but it’s the main reason many cruisers prefer bottled water for drinking while using tap water for brushing teeth and showering without concern.
Practical Tips for Staying Hydrated
If you’re comfortable drinking the tap water, the buffet and dining room water stations are your most convenient free option. These pull from the same ship supply but are often run through additional filtration at the point of service.
If you’d rather not rely on tap water, most cruise lines sell bottled water packages that you can pre-order before your trip, often at a lower price than buying individual bottles onboard. Some lines allow you to bring a limited number of bottles in your carry-on luggage. Bringing a refillable bottle with a built-in filter is another option that splits the difference: you get the convenience of tap water with an extra layer of filtration for taste and peace of mind.
Passengers with compromised immune systems or those traveling with infants may want to take extra precautions, since even small variations in water quality that wouldn’t affect most adults can matter for vulnerable groups. In those cases, sealed bottled water is the most conservative choice for drinking and mixing formula.