How We Make Our Own Freshwater on a Boat (and Never Run Out!) -

Straight up, the answer is… a desalination unit! You may or may not know what that is, but in simple terms, it turns salt water into fresh water.

Is that making more sense? We’re only two sentences in, so I don’t blame you if you’re still confused! Let’s fix that and dive into how we make our own freshwater onboard and never run out!

Sort-of related:

How to Anchor Your Boat Safely

Surfboards on a Catamaran: How We Store and Care for Them

The Process

Before we talk about what we use and how, let’s go over the water-making process in basic-ish terms.

First, salt water is sucked in through a hole under the boat. It’s then pushed through two pre-filters (a 5-micron and a 20-micron, for those interested). From there, it moves into the membrane—a large filter packed with straw-like fibers that work to separate the fresh water from the salt.

Once it’s through the membrane, the water is divided into two streams: clean, fresh drinking water and super salty brine water.

Image explaining the basic process of turning salt water into freshwater on a boat.

The salty water is pumped back into the ocean, while the fresh water flows into our tanks for storage.

Right, that’s a super basic rundown!

The Equipment

Now that we know the process, what about the gear that makes it happen?

Pre-filters

These start the filtration process, removing sediment, chlorine, and organic matter. This is crucial because if those things made it to the membrane, they could clog it up.

Pump/Motor

This powers the high-pressure pump (coming up next). Ours is pretty loud, but it keeps the whole system running.

High-Pressure Pump

This pump pulls and pushes water where it needs to go, ensuring the right PSI for filtration.

Membrane

Ahh, the real MVP!

The membrane ensures that only fresh water comes through. Think of it like a sieve—it removes all the minerals, microbes, and other stuff we don’t want, letting only pure water molecules pass.

Image of our water maker up in the forepeak of our vessel.

Tanks

Once we have fresh water, we need somewhere to store it! On Happy Days, we have two 450L tanks—900L total. That’s usually enough to last several days, but we’ll get into water consumption in a minute.

Brand & Model

Our whole water maker setup—enough to keep all six of us hydrated and comfortable—is an Osmosea CL 200. It’s a pretty big one, producing 200L per hour.

On our old boat, Torea, we had a much smaller Rainman watermaker, which made closer to 60L per hour. It was simpler, and if we were to buy a new one, we’d probably go for a more simple setup than our current one.

Water Consumption

All right… how much water do we actually use?

Onboard, we do all the usual things—washing clothes, dishes, showers—so how do we manage our water use and make sure we don’t run out?

Some water-saving tips:

Showers: The trick is rinse, turn off, soap up, rinse again—quick and efficient! (Bonus: no time to stand there and daydream.)

Laundry: We have a small washing machine that allows us to do 15-minute loads—just enough to get clothes clean without wasting water.

Dishes: We don’t have a dishwasher, but we also don’t use salt water to wash dishes. Instead, we fill the sink with fresh water and wash efficiently.

Image of a shower head explaining how to save water.

The “Scale of Saltiness”

Where do we rank on the Scale of Saltiness?

1 = You only use fresh water for drinking.
10 = You don’t think about water consumption at all.

I’d say we’re around a 5 or 6—not extreme water savers, but definitely mindful!

Some quick stats:

Onboard, each of us uses about 26L per day, including everything—washing, dishes, showers, drinking.

For all six of us, that’s 156L per day. Sounds like a lot? Let’s compare that to land-based water use per person per day:

USA = 300L
Australia = 180L
UK = 150L

Yikes! I hadn’t looked that up before—it’s kinda crazy, hey?! Compared to that, I think we’re doing all right. But it has taken practice!

Image of an average American house explaining how much water the average person on land uses.

If you’re on land and love long showers, boat life might take some getting used to…

FAQs

Does the water taste salty?

Ahh, no—that would be gross.

Is desalinated water healthy long-term?

We’ve been drinking and using it for years with no issues. However, desalination removes everything, including good minerals like iron that can be present in tap water.

To fix this, we recently added a remineralizer to our drinking water tap. We don’t notice a difference, but if it’s adding good minerals, why not?

Can we make water while sailing?

Yep! On longer passages, we still need the same amount of water—though a few people sometimes feel too queasy to shower.

What happens if the water maker breaks?

We try to fix it ASAP. But just in case, we carry tons of spare parts. If we couldn’t get it working, we’d have to go to land, get water, and bring it back. Lots of boats without a water maker do this regularly!

How often do we make water?

We run the water maker every 2–3 days, keeping at least one tank half full at all times. That way, if something goes wrong, we have a buffer.

Final Thoughts

We’ve covered the desalination process, the equipment we use, water-saving tips, and some surprising water-use stats. If you’re interested in more tips and explanations, here are some good places to find them: Reverse Osmosis Explained, How Our Family Of Six Lives Off-Grid, Water Saving Tips For Homes, and Water Saving Tips For Boats.

So… would YOU survive on a boat with limited water? Rate yourself on the Scale of Saltiness and let me know in the comments!!