Cruise passenger can’t believe exactly where all the ship's water comes from

Cruise ship holidays aren't for everyone, but even those who become hooked on them for life have to start somewhere.

And much like any kind of holiday, there are certain rules, habits and information you'll come across with time. For one, don't mention the Titanic.

One man taking his first cruise is TikTok star Marc Sebastian, who has spent the last 18 days documenting his time on board Royal Caribbean's the Serenade of the Seas.

It's a 22-year-old vessel currently on a nine-month continuous tour of the entire world.

Marc settled in for the 18-night South America-Antarctica leg of the cruise and took to TikTok multiple times a day with updates on what life was like on board.

As the holiday came to end, he uploaded a new clip with some final thoughts on the trip.

After revealing his shock at not being able to mention the Titanic onboard any boat (bad luck, apparently), he moved on to the issue of water.

Marc said: "Here's a list of things I have learnt about cruising while I've spent 18 nights on this floating retirement home with a Cheesecake Factory attached.

"Did you guys know that cruise ships fill their pools with sea water?

"If you to look me dead in the eyes and say 'yeah I did know that cruise ships fill their pools with sea water'.

"I don't know how in head I thought they were filling them but what I didn't think they were doing was filling them with sea water.

"And then what? Treating it? And then just kind of throwing it into the ocean?

"And let me tell you they are not shy about sucking the whole pool down right back into the ocean and then sucking up some new water."

Mind blown, right?

Marc even reveals that the Serenade of the Seas had plans to get rid of its pool waters when in Antarctica and 'suck up some Arctic water' to do cold plunges on board the ship.

He said: "My body would have literally gone into shock, I would not have come out of that alive, but other people were going to do it."

People were quick to comment on Marc's revelation regarding the water, with it becoming apparent that this isn't just the policy when it comes to pool water but pretty much all water for the vessel.

We're talking tap water, ice in your drinks, toilet bowls, showers. The list goes on.

One person said: "I only know this because when I was a kid we did a cruise and they didn’t have as good of filter systems and it was salt water. I hated it."

Another wrote: "Pools are but hot tubs aren’t and it burns when you switch from one to the other."

A third added: "I only knew the pool thing because some one threw up in the pool and got glass in it when I was on a cruise and they emptied, cleaned and filled it."

Over on the Royal Caribbean website the company says 'water is a precious resource, both on our ship and off and we go to great lengths to ensure it’s used efficiently'.

The company says: "Royal Caribbean Group ships produce 90% of the freshwater used on board via desalination or reverse osmosis.

"This water is used for drinking, showers, sinks, toilets, kitchen galleys, pools, technical machinery, and spas aboard our ships."

Desalination systems boils and evaporates seawater, which is then condensed into freshwater. While this process is energy intensive, Royal Caribbean says it account for this by repurposing engine waste heat or steam from exhaust gas boilers to heat the water.

Reverse osmosis is a system that creates freshwater by pumping seawater at very high pressure through a filter or semi-permeable membrane that only water

molecules can pass through.

So there we have it. As Jesse Pinkman would say: "Yeah science, b***h."