The backend of a ship - Water management - Cruise Ship Hospitality Expo

The backend of a ship – Water management

Royal Caribbean Oasis of the Seas at Cadiz Shipyard
Royal Caribbean’s ships produce potable water in multiple ways

We’ve already explored the statistics and logistics behind food management onboard cruise ships – but as well as food, a floating city requires water to keep its citizens happy. Below we’ll dive into how a cruise ship manages to quench the thirst of thousands of passengers, and how wastewater is dealt with onboard.

Water on board

On Royal Caribbean ships safe, clean, drinkable water is provided in three ways. The first of these is through bunkering it – loading it in port and storing it. The water is tested while it’s being brought on board for pollutants and microbials, and once checked is treated and chlorinated, ready for drinking.

However, bunkering all the water for a multi-day cruise on a high-capacity ship isn’t feasible – it weighs a lot and takes up sorely needed space – so how does a ship avoid running out of water? Nick Rose, environmental regulatory lead, environmental stewardship for Royal Caribbean explains the second method. Named either steam evaporation, flash evaporation, or steam desalination, the process uses heat from the ship’s engines to boil seawater brought on board. The water is heated by excess steam from the engines to remove the salt, before being condensed into distilled purified water. Minerals are then added to the water to give it the familiar water flavour, before being sent for chlorination to ensure there is nothing growing in it.

On Carnival cruise ships, approximately 79% of the water used onboard is from seawater, with the remaining 21% bunkered; on Norwegian ships, 15% is bunkered, 43% is from steam evaporation, and 43% is from a process called reverse osmosis – a more modern and technologically advanced process of creating potable water.

In reverse osmosis, seawater is brought onboard and pushed through a semi-permeable membrane, resulting in pure water. Royal Caribbean say that on average, its guests consume around 55 gallons of water each per day. This is less than the US average by almost half! Water is essential to the running of the ship, so every possible bit needs to be saved – so what are cruise lines doing to keep the usage down?

Norwegian Cruise Line Encore at Sea
Norwegian’s vessels feature advanced water purification systems to clean wastewater prior to discharge

Saving Water

To ensure ample pressure in the showers and sinks whilst also saving water, Royal Caribbean ships aerate the water supply as an alternative to pumping out high volumes. Forcing air through shower heads and taps allows guests the ability to shower comfortably while decreasing the amount of water used.

The cruise line also reuses condensed water wherever they can. A ship sailing in the warmer parts of the Earth will continuously produce a lot of condensate water – where the air is cooled down in parts of the air conditioning units, the humidity in the air becomes liquid water. This accumulates in a collection pan at the bottom of the AC units and is then reused in the laundry system on board.

Carnival’s efforts to save water include constantly updating water usage systems to the most efficient variants; encouraging guests to reuse towels and sheets to reduce laundry load; and training crew on water efficiency practices.

Carnival also make efforts to reduce the impact of water procurement at the ports they dock at – by decreasing the amount of water bunkered, the amount of water needed at port is reduced. The cruise line also ensures they are not purchasing water from those places with a water scarcity risk, such as when a drought is experienced.

But not all water can be reused – so what happens to wastewater?


On Royal Caribbean ships, Nick Rose explains that the treatment systems exceed the requirements of all international regulations. First, the ‘grey water’ – wastewater from galleys, laundries and bathrooms – is mixed with the ‘black water’ – lavatory wastewater – before being sent to bio reactors. Within these, bacteria digest anything unwanted, and the water is then disinfected with UV radiation – an alternative to chlorine and other chemicals that could be harmful to sea-life. After being monitored for any bugs, the remaining water is ready to be discharged into the sea.

On Norwegian’s ships, wastewater is treated with Advanced Wastewater Purification systems (AWPs) to meet or exceed international standards before being discharged. All of their newest ships are equipped with AWP technology that meets the Baltic Standards, and all wastewater is tested by a third party every quarter.

The new Virgin Voyages vessel Scarlet Lady takes the same approach, using advanced wastewater treatment systems onboard to process black and grey water, exceeding international regulations and ‘surpassing land-based treatment facilities.’ Scarlet Lady will also feature water-efficient dishwashers and laundry equipment, as well as low-flow water fixtures and vacuum toilets to save water.

The way the water flows

Cruise ships are clearly advanced machines when it comes to water efficiency, realising the importance of saving and reusing water where possible. Developments in reverse osmosis technologies, being adopted by more and more ships (Virgin Voyages’ Scarlet Lady will feature reverse osmosis desalination) means a reduction in the amount of bunkered water onboard – saving space, money and the need for a supply at water-scarce ports.

If you have a piece of equipment that can help cruise lines reduce their water usage, make sure you’re exhibiting at Cruise Ship Hospitality Expo on 16 – 17 June!

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