Do You Need a Watermaker for Boat Living?

Published Categorized as Boats

A watermaker is one of the miracles of modern cruising life. These marvels of modern technology make fresh drinking water out of salt water – every sailor’s dream, right? You might even be thinking that since such a thing exists, surely every boat must have one. 

But the answer is more complicated than you think. Small-boat cruisers have been traveling all over the world for decades without watermakers. It’s not because they couldn’t get them, but instead because they are costly and complicated gizmos. For many cruisers, foregoing a watermaker meant a year more of traveling they could do on the money saved.

When we first got into long-term cruising, we wanted a water maker on our boat so that we could be completely off-the-grid capable, no matter where we went. While it’s possible to fill up your tanks at marinas, it’s often an extra hassle. Plus, we find that many marinas have low-quality well-water or funky municipal water. Having a watermaker means you have one less consumable item onboard to track and worry about, and no need for bottled water or other expenses.

So, should every boat have a watermaker? Here’s a look at how the wonderful watermaker works and how to decide if one belongs on your vessel.

Table of Contents

watermaker for boat

What is a Watermaker?

A watermaker is an expensive gadget that is a freshwater maker for boats. You feed it seawater, and out comes drinkable pure freshwater. Another word for this miracle of modern technology is the reverse osmosis desalinator.

The watermaker works by pumping in seawater and filtering it through progressively finer and finer filters. The final stage of filtration–the reverse osmosis membranes–filters out even the dissolved solids (like salt) from the water. 

The resultant water is exceptionally pure. Exactly how pure it depends on the health of your membranes and filters. But the water made by a boat desalination machine is cleaner and purer than nearly all bottled or municipal water sources. 

The pump needs to be powerful to filter the water to this extent. As a result, there are two types of watermakers for boat buyers. First, low-output units use smaller amounts of power–an excellent choice for battery and solar-powered boats. And then there are high-output units that use a lot of electricity, which are great on boats with powerful generators. 

Reasons You Might Want a Desalinator for Boat Life

Some sources talk about a watermaker providing unlimited fresh water all the time. This might be the case for those with a yacht water maker, capable of hundreds of gallons per day. But to make that happen, you need a powerful full-time generator on board, and you need to run it all the time. That’s not realistic for most of us, nor is it desirable. 

If it’s not unlimited, is it worth it? The question varies for every boat and crew out there. Installing a desalinator for boat life has its advantages and disadvantages.

Advantages to Having a Watermaker

  • Convenient–less reliance on finding fresh water from docks
  • Many marinas have poor quality water from municiple, well, and RO supplies
  • Requires you to carry less water, improving your sailing performance—a big plus for long-distance multihulls
  • Allows you to use more fresh water–more showers, more boat cleaning and rinses, more laundry, more dishes

Watermaker Disadvantages

  • Extremely expensive to purchase
  • Difficult plumbing install—usually requires a haul-out
  • Cost can easily double for professional installation
  • Difficult to maintain—must be used regularly and flushed or cleaned often
  • Requires consumable items and spares to be carried aboard
  • Large, bulky, heavy item
  • Uses a lot of electricity
  • One more expesnsive component to break and require replacement parts
  • Many sailors only use them in the cleanest offshore waters—may have to resort to shore-side fills if you’re in a dirty harbor

Energy Efficiency for a Big Boat Watermaker vs. Smaller Sailboat Watermaker

One tricky thing about researching watermakers is how hard it can be to differentiate between those models intended for yacht water maker applications and those meant for us little guys. 

It’s tempting to focus on the “gallons per day” measurement. This is undoubtedly where the sales literature draws you in. But this number usually assumes a few things. For example, will you be running your watermaker 24/7 while on the water? Will you have the power supply to make that happen?

On our sailboat, this isn’t the case at all. In fact, it’s almost the complete opposite of how we use it. Instead, we switch the unit on when we need to make water and turn it off when we’re done. We pay close attention to our tank levels and consumption and use the watermaker sparingly.

You can draw a line between the types of watermaker users in this way—those using their watermaker constantly and those that turn it on only when necessary. The deciding factor is how much power they have to spare for this big power-hungry operation.

If your yacht has an inboard electric generator, then it’s safe to say you can find and install a watermaker you can turn off and on at a whim. Generators are wonderful things, and they allow you to run big power consumers constantly—just as long as your generator is constantly running.

yacht watermaker

Not everyone has or wants a generator onboard, however. They are noisy and smelly (yes, even expensive inboard ones). They are another engine, and with them comes all of the cost and trouble of maintaining another engine. Finally, they’re heavy and take up a lot of space in a small boat.

So what do you do if you don’t have an AC generator? If you live off-the-grid using renewables like wind and solar, you’ll have to do some math. You are likely very familiar with this math if you’re already out there living this life.

Every yacht consumes a certain amount of watts every day. It’s the amount of energy you use from your batteries by way of your refrigerator, lights, electronics, and maybe the computer and phone you need to keep charged. The more toys you have, the more energy you need. The watermaker is just another toy.

To live off-the-grid, you have to have some way to supply the used watts back into your batteries. This is where wind and solar come in. But what about when it has been cloudy and calm for days, making the batteries get low? Do you have some high-output option (like a generator or alternator) to recharge the batteries? 

Boats’ electrical setups like this vary significantly in complexity. There are plenty of boats out there with a single small solar panel and 300ah of house batteries—they’re living simply and cheaply. A watermaker that works on a system like this is a tough sell. 

Other boats have set up 1.5 or 2 kilowatts of solar panels that feed a kilowatt or more lithium batteries. They’re living life with every luxury—air conditioning included—all without the help of a generator. A watermaker is an easy upgrade on a boat like this.

Boat power systems vary so widely, from the smallest of the small to the biggest of the big, that it’s impossible to generalize which watermaker is best for everyone. Instead, it all comes back to the robustness of your electrical system. So first, you need to know how many watts you can spare for water-making duties and then find the highest output unit that gets the job done.

boat power systems vary

Watermaker 101 — How Does a Watermaker Work?

All watermakers are remarkably similar. They all function in the same fundamental way with the same basic parts to produce pure drinking water. 

1. Inlet

First, the water is brought into the boat for use by way of a through hull below the waterline. Its first stop is a strainer, which filters out big stuff like seaweed and jellyfish.

2. Low Pressure Pump

The water is pulled in the through hull and strainer by a low-pressure water pump. This is like the one on your engine, and it usually has a replaceable rubber impeller of the same type. It’s generally driven by the same power sources as your high pressure pump.

3. Seawater Filter

Next, the water goes through one or more paper pre filters. This eliminates the sediments and larger contaminants in the water. Some systems have more than one filter. 

This filter is the most important one to watch. If you’re running your watermaker in cloudy or murky water, it can get gunked up quickly. If it’s gunked up, the pump will have trouble pressurizing your membranes to the proper PSI. So you need spares onboard.

4. High Pressure Pump or Pressure Supply Unit

The next stop is the high-pressure pump. To work, most reverse osmosis membranes need a supply pressure of around 800 PSI (pounds per square inch). This is roughly equivalent to a pressure washer. 

The high-pressure pump is the part of the unit that requires all the power. If your unit is electric, it will be attached to a drive motor. You can get motors that run on 12, 110, or 220 volts. There are also engine driven watermaker options if your system doesn’t have enough electricity to spare.

5. Reverse Osmosis Unit

Water is then sent to the membranes, where the real filtering is done. Much more seawater is being supplied to the membranes than will come out as freshwater. The excess is discharged back into the ocean as brine. This is usually sent out via an above-the-waterline discharge through hull.

When you first start the pump, all water will pass through the membranes and out of the brine discharge. To begin the water-making process, you close a valve that forces the water through the membranes. Clean water will come out of the product water line, while brine will continue to be discharged overboard.

 You’ll often find yourself flushing or cleaning the unit, so you want to make sure you test the unit’s efficiency regularly. Most people use a TDS (total dissolved solids) meter to do this. Place some product water in a cup and dip the end of the meter into it. Most watermakers put out water that is less than 500 ppm. You’ll notice your membranes getting less and less efficient as time goes on, and you can see this loss by an increase in the TDS reading.

The freshwater product line is then diverted straight to your ship’s tank. You can add as much as you want—for as long as you want to run the unit.

Dow Filmtec SW30-2521 Seawater Desalination Reverse Osmosis Membrane

6. Flushing Option

Flushing, cleaning, pickling, and winterizing are essential parts of watermaker ownership. If you allow raw seawater to sit in your system and membranes for too long, it will foul up the system. Eventually, it will stop working, and you will destroy your membranes. You can solve this problem by flushing after every use or weekly if you use it often.

Flushes should only be accomplished by running the cleanest product water back through the system. Most watermakers are set up with the plumbing to accomplish this by turning a few valves. This purges seawater from the system and ensures nothing nasty will settle in your membranes and pump. Flushing will keep the unit clean and ready to go for a few weeks.

If you’re leaving the unit for longer, you can pickle it. The pickling process is just like the flushing process, except you put a particular chemical (sodium metabisulphite) in the clean water that sits in the unit. A pickled watermaker can be stored for up to six months. 

Finally, like all marine systems that store water, a watermaker needs to be winterized if it will sit in sub-freezing temperatures. Most units use the standard “pink stuff”—propylene glycol. Check your owner’s manual, though, just to be safe.

How to Choose the Best Marine Watermaker

If you want to add a watermaker to your boat, you have a few decisions to make. You’ll need to look at the unit’s power consumption, freshwater output, and how you intend to install it.

Power Requirements and Energy Consumption

The most crucial part of watermaker selection is figuring out how you intend to run it. No matter its size, every boat has constraints on how much power it can produce. 

If your boat has a generator, it makes the most sense to pick a watermaker that will run while the generator runs. You’ll need to consider your genny’s output and subtract the other tasks that it needs to do. How much power do the battery charger use, the air conditioners, and any other accessories that will be running at the same time as the watermaker? 

If you have an off-the-grid sailboat that operates on battery power, augmented with wind, solar, or hydro power, you will be familiar with how many watts you use on any given day. A watermaker will add a substantial amount of draw on your electrical system, so you’ll need to decide if you opt for a low-capacity 12-volt unit or a higher-capacity 110/220-volt system that you don’t run as long. To run a 110/220-volt system, your boat will need to have an appropriately sized inverter.

If, after doing the math, your electrical system is not up for the water-making game, you aren’t out of options. Your first option might be to pick up an inexpensive 2000-watt portable gas generator/inverter. These are handy to have to charge your batteries, relatedly inexpensive, readily available, and powerful enough to make a lot of water. Of course, you’ll have one more bulky item to carry, plus you’ll have to feed it gasoline every few hours of operation.

Rainman makes a portable watermaker that includes a built-in gas engine. This foregoes the gas generator but still requires you to carry gas onboard. A few engine-driven options are also on the market, although those have become rare as yacht power systems have advanced.

Output

Once you know how you will power it, the next job is to shop for the unit that gives you the most water (in gallons per hour GPH) for the amount of power (in watts) you’re willing to sacrifice. 

A low-output 12-volt system will usually make between five and ten gallons per hour. A high-output system running with a more powerful 110 or 220-volt pump can put out 30 gallons per hour or more.

You’ll also find yourself balancing the cost of units versus how many GPH they produce. Don’t forget that while a high-output system might cost a little more, you’ll have to run it a lot less. In the end, this might make more sense financially as well as from an electrical standpoint.

Installed or Portable

Don’t forget about the trouble and cost of installation. Rainman makes a line of watermakers that are hard to beat for one simple reason–they’re completely portable. They consist of two cases. One is the pump, and one is the membrane. With a few hoses and an electrical hookup, you can make water anywhere. 

The problem with these systems is that they require a lot of setup for each use. The cases are bulky and heavy. You need a lot of space to store them—more than an installed system would use up.

On the other hand, an installed system can be placed in otherwise unused lockers or under the floorboards—where it is out of the way. But an installed system is challenging to put in. It’s a major boat project. It will require a new through hull or two, lots of plumbing, and running hoses and power wires. If you’re hiring a professional, expect the installation to cost at least as much as the price of the watermaker.

Emergency Sailboat Desalination Options

If you’re looking for a water maker for sailboats operating offshore or on an ocean crossing, but only for emergencies, there are extremely low-output models available. The problem with these is that they are still costly. By the time you justify the expense of an emergency desalinator, you’ve spent a significant portion of the cost of a normal one for regular use! 

For purely emergency use, the Katadyn Survivor series is the go-to. The Survivor 06 is rated for six people in a survival situation. It has a hand pump for manual operation that makes a half-gallon of water for every hour of pumping.

Do You Need a Water Maker for Boat Life?

Everyone wants to know if a watermaker is worth it or if you need it. The answer depends on the type of cruising you do. If cruising is about “going small and going now,” then no, you certainly don’t need the expense, complexity, weight, and hassle a watermaker aboard adds. 

But if you’re setting up a boat for off-the-grid living and looking to minimize your reliance on those shore-side items, a watermaker can make some sense. You’ll still have to find gas or diesel occasionally, but with a good watermaker, you might never need to worry about finding clean water again.

Boat Watermaker FAQs

Is a watermaker worth it?

The answer is yes, but there are several “buts.” Watermakers make cruising life easier in general, and that’s a good thing. They give you the option to replenish your water tanks without visiting the shore. So if off-the-grid living with minimum resupply trips is your goal, a watermaker should be on your list.

But here are some of the downsides of owning a watermaker.
They are extremely expensive to purchase and install. 
They need regular use to keep working—they do not respond well to being left idle for weeks at a time
You must be religious in your flushing and pickling schedule
They require a lot of electrical power—a generator is best
They are heavy and bulky
They work best when provided clean water—usually only found in the open ocean

What is a watermaker on a boat?

A watermaker, also called a reverse osmosis desalinator, is a machine that turns raw seawater into safe, clean drinking water.

How much do watermakers cost?

Most watermakers for small boats cost between $3,000 and $5,000 before installation. There are some cheaper DIY options available, but all watermakers are costly. Not only are the parts expensive, but the installation in your boat is a big project that will probably require a haul-out.

Can you drink water from a watermaker?

Yes. Although you should always test watermaker water before drinking, the product water should come out completely safe to drink. Any pathogens or organic material that might be present are much larger than the dissolved salt molecules flushed out by the system. As a result, the product water from a well-maintained watermaker will produce some of the safest and cleanest water you can find anywhere–usually far cleaner than tap or even bottled water.

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