If you've spent any time living on a boat or off-grid, you know that finding fresh water is a constant battle, which is why I finally decided to look into a rainman portable watermaker. For the longest time, the ritual of "water runs"—hauling heavy jerry cans back and forth in a dinghy or praying the next marina had a working hose—was just part of the lifestyle. But honestly, it gets old. You start rationing showers and washing dishes in salt water, and eventually, you just want the freedom to stay out at anchor without checking the tank levels every five minutes.
The rainman portable watermaker changed the math for a lot of us because it doesn't require you to drill holes in your hull or commit to a massive, permanent installation. It's a simple, modular system that does one thing really well: it turns the ocean into drinking water without the headache of a complicated setup.
What Exactly Is This Thing?
At its core, the Rainman is a reverse osmosis (RO) system, but instead of being tucked away in a cramped engine room, it's housed in two (or sometimes three) ruggedized plastic cases. These look a bit like heavy-duty toolboxes or Pelican cases.
The system is split into two main parts. First, you have the Pressure Supply Unit (PSU). This is the "heart" of the machine that sucks up the seawater and pushes it through the system at high pressure. Second, you have the Reverse Osmosis (RO) Case, which contains the membranes that actually filter out the salt and minerals.
The beauty of this design is that you only bring it out when you need it. When you're done, you pack it away. For those of us with smaller boats or people who don't want to deal with the maintenance of a built-in system, this modularity is a massive win.
Powering the Beast: Petrol vs. Electric
One of the coolest things about the rainman portable watermaker is that you aren't stuck with just one power option. When they first hit the scene, they were famous for their gasoline-powered (petrol) model. It uses a little Honda motor to run the pump.
The gas version is a beast. It's completely independent of your boat's electrical system, which is huge if you don't have a massive solar array or a built-in generator. You just sit it on the deck, pull the cord, and it starts making a ton of water—up to 140 liters (about 37 gallons) per hour. That's fast. You can fill your whole tank in the time it takes to eat lunch.
Of course, if you'd rather not carry extra gasoline on board, they have AC and DC electric versions too. The AC version is great if you already have a portable generator like a Honda EU2200i. You just plug it in and let it rip. The 12V DC version is a bit slower, but it's silent and runs right off your battery bank, which is perfect for those sunny days when your solar panels are putting out more power than you can use.
Setting Up and Making Water
Using a rainman portable watermaker is surprisingly straightforward, though it does take a few steps to get the hang of it. You start by tossing the intake hose overboard. It's got a weighted pre-filter to keep out the seaweed and bigger bits of junk. Then, you connect the high-pressure hose between the pump unit and the membrane unit.
Once you've got your hoses sorted, you prime the pump and start the motor. There's a pressure control valve that you slowly turn to ramp up the pressure. You'll see the needle climb on the gauge, and once it hits the sweet spot, fresh water starts trickling out of the product tube.
I usually taste the first bit of water (once the TDS meter says it's good) just because there's something satisfying about drinking water you just pulled out of the sea. After that, you just stick the hose in your deck fill, and you're good to go. It's not "automated" like some of the $10,000 built-in systems, but there's something nice about being involved in the process. You can see exactly what's happening, and there are fewer electronic sensors to fail on you in the middle of nowhere.
Why Go Portable Instead of Built-In?
You might be wondering why someone wouldn't just install a permanent watermaker. To be fair, built-in units are great because you just flip a switch. But they come with a lot of baggage. You have to install a dedicated thru-hull fitting, run plumbing through the entire boat, and find a place for the membranes where they won't get too hot or too cold.
The rainman portable watermaker sidesteps all of that. If you sell your boat, you take the watermaker with you. If the pump needs a repair, you can take the unit to a shop instead of having a technician crawl into your bilge at $150 an hour.
Also, it's a great backup. I've met sailors who have a fancy built-in system that broke down in the Marquesas, and they ended up buying a Rainman just because it's so reliable and easy to fix. Since it uses standard parts and filters that aren't proprietary, you aren't held hostage by a single manufacturer when you need a new O-ring or a filter.
The Reality of Weight and Noise
I'm not going to sugarcoat it: these units have some weight to them. The gasoline PSU weighs about 25kg (55 lbs), and the RO case isn't exactly light either. If you have a bad back or a really high freeboard on your boat, lugging these out of a locker every time you need water might feel like a workout.
Then there's the noise. If you're running the gasoline version, it sounds like well, a small lawnmower. It's not deafening, but you probably won't want to run it at 6:00 AM while your neighbors in the anchorage are trying to sleep. The electric versions are much quieter, but you still have the hum of the high-pressure pump. It's a trade-off. Personally, I'd rather listen to a motor for an hour than spend six hours rowing 20-liter jugs to a beach tap.
Maintenance and Keeping It Happy
The biggest killer of any watermaker is letting it sit with salt water inside. If you don't use the system for a few days, the salt can crystallize and the biological bits in the water can start to get smelly.
The rainman portable watermaker makes the "fresh water flush" pretty easy. You just run some of your produced fresh water back through the system for a minute before you shut it down. If you're putting it away for a long time (more than a week or two), you have to "pickle" it. This just means circulating a food-grade preservative through the membranes to keep them from growing mold or bacteria. It sounds technical, but it's really just a five-minute job once you've done it once.
Final Thoughts
Is a rainman portable watermaker cheap? No, it's a significant investment. But when you look at the cost of a permanent installation plus the labor, the Rainman starts to look like a bargain. More importantly, it gives you peace of mind. Knowing that you can make your own water—even if your boat's main electrical system is acting up—is a huge confidence booster for long-range cruising.
If you're the type of person who likes simple, robust gear that does its job without a bunch of fancy bells and whistles, this is probably the right call. It turns a chore that used to be a major headache into just another part of the routine. And honestly, there's nothing quite like taking a long, cold shower on a hot day in a remote anchorage, knowing you have all the water you could ever need right there in those blue boxes.