Where Do Boats Get Fresh Water?
Welcome to a new series of "How does this thing work on a boat?" All those things that have you wondering whether it's different out on the water than it is on land—we're going to uncover several of them!
The first one: where do boats get fresh water? Let's dive in.
The short answer
The short answer is: we have a reverse osmosis watermaker. That's a fancy way of saying we have a machine that turns salt water into fresh water. Yep, that actually exists!
Now, I know that hardly answers your question, so let's run through some more details.
How it works
As simple as "turning salt water into fresh water" is to say, it actually takes quite a few moving parts to make it happen.
It goes roughly like this:
The motor and high-pressure pump pull salt water in through the bottom of the boat. It then goes through two pre-filters before being pushed through our big membrane... and when it comes out the other end? Fresh water.
Now, I don't design, build, or know all that much about desalination or reverse osmosis systems, so I'm not going to pretend I do. Hopefully I know enough to have it all make sense!
The parts involved
Like I mentioned, there are quite a few different parts involved in the process. Here's the journey from salt water to fresh water:
Thru-hull. The salt water comes in through a hole in the boat. This is where the process begins.
Pipes. Kind of obvious, but oh well—they carry the water through the system to the...
Pre-filters. We have two pre-filters: one 5-micron and one 20-micron. These act as the very first filters for the salt water before it reaches the membrane.
Membrane. Despite its name, the membrane has absolutely nothing to do with big thinking. It's actually pretty simple: hundreds of tiny straw-like filters designed to remove almost everything from the water—including the salt. Amazing, right?!
High-pressure pump. To get the water through the membrane fast enough, it needs to be under really high pressure. Hence, we have a pretty decent-sized high-pressure pump. Another thing about high pressure—you need high-pressure fittings too. These can be surprisingly tricky to find, so we carry plenty of spares.
Motor. And, of course, the motor that runs all of this business! It's what I'd call a relatively normal motor: we give it power (generally from the solar or generator), and it powers the high-pressure pump for us.
Water tanks. Lastly, once the salt water has been converted into fresh water, it heads into our water tanks, where we can store up to 900 litres. Our rule is to always try to have one tank full (which is 450L), so whenever we empty one, we fill it straight away (or at least that's the theory).
Our exact watermaker
Our whole setup is from a company called Osmosea, and we have the Osmosea CL 200.
It produces around 200 litres of fresh water per hour and is an absolute beast of a watermaker, to be honest. Most boats might have something closer to a 70-litre-per-hour watermaker, but hey, this is what we got—and we've definitely grown to like it.
Spares we carry
This is our only source of fresh water when we're out on the ocean or in remote anchorages, so it has to work.
As you can probably guess... it doesn't always work.
When something goes wrong, we're left trying to fix it as quickly as possible so we don't run out of water.
Unfortunately, this has happened often enough that we've learned exactly what spares we need to carry.
High-pressure fittings. These are our biggest nemesis when it comes to the watermaker. I've lost count of the number of times Kris has climbed down into the forepeak to sweat it out while trying to figure out what's gone wrong. Bella too, because it usually takes two people holding different tools and parts. We carry several different fittings specific to our watermaker—a small elbow that blows often enough (we have at least 10 now), a larger elbow that fits onto the end of the membrane and occasionally leaks, and plenty of other bits and pieces.
A high-pressure pump. Yep, we now carry an entire spare high-pressure pump. It took some deliberation because it's so heavy, but in the end we decided it was a must.
A new membrane. Yep, one of those too. We've had to replace it before—twice, actually.
Loads of pre-filters. These are routine replacements anyway, but they definitely belong on the list. We carry plenty of both the 5-micron and 20-micron filters.
Summary
So there you have it—that's how we get fresh water on the boat. Maybe it's a bit more complicated than you expected... maybe not!
While this is how we do it, plenty of other boats do things differently. Some people head ashore, fill jerry cans with fresh water, and carry them back to the boat. Others rely on collecting rainwater.
For us, though, having a watermaker is by far the best option.
I really hope this post helped you understand boat life just a little bit better! If you've got any thoughts, questions, or your own stories to share, leave a comment—I'd love to hear them.