Selection of watermakers for blue water yachts

Independence through water from the sea

As bluewater sailors, we are almost always surrounded by the best, clearest water. Unfortunately, we can't do much with the saltwater. The salt content is too high even for cooking potatoes or pasta.

Water requirements – How much water do I need?

There's no general answer to this question. We've met crews who attempt an Atlantic crossing with just a few hundred liters of water, and others who burn the same amount of water in just a few days. A good rule of thumb is to expect water consumption of 10 to 15 liters per person per day. More or less is always possible. This should be taken into account when choosing a watermaker.

What exactly is a watermaker and how does it work?

Watermakers, also known as desalination systems or reverse osmosis systems, are crucial systems for boats that spend long periods at sea, as they allow drinking water to be extracted from seawater. Here's a simplified illustration of how these systems work:

1. Suction of sea water: First, sea water is taken on board using a pump.
2. Pre-filtration: To remove larger particles and impurities, the water first passes through one or more pre-filters.
3. high pressure pump: The pre-filtered water is then put under high pressure using a high-pressure pump, which is necessary to enable the next step of reverse osmosis.
4. Reverse osmosis membrane: Under high pressure, the water is forced through a semipermeable membrane. This membrane allows only water molecules to pass through, while keeping out salt, bacteria, viruses, and other contaminants.
5. Formation of two water streamsAfter the membrane, the water splits into two streams. One consists of treated water with a low salinity, which is stored for use on board, and the other is a wastewater stream with a high concentration of salt and contaminants, which is pumped overboard.
6. aftercare: The purified water can now be passed through further filter systems, such as activated carbon filters or UV lamps for disinfection, to remove any remaining flavors or microorganisms.
7. Water storage: The treated, purified water is stored in clean tanks and is thus available for consumption.

The efficiency and capacity of a watermaker depends on numerous factors, including the size of the membrane, the pressure at which the high-pressure pump pushes the water through the membrane, and the overall quality of the system used. Regular filter replacement and maintenance of the system are also important to ensure its longevity and reliable operation.

There are numerous different systems and manufacturers on the market. They all share the same operating principle: Saltwater is forced into a membrane at high pressure. A small portion of the water becomes drinking water because the membrane prevents the salts from passing through. The majority of the water is pumped back overboard with a higher salt content. These membranes are industry standard and, if properly treated, will last for years.

Classic systems with high-pressure pump

The heart of traditional systems is a high-pressure pump operating at 230V and typically consuming around 1,5 kW. This power must be available for extended periods, usually several hours. For this reason, traditional watermakers are often operated when the main engine or a generator is running, or when the solar panels are at their maximum output during midday. The pumps are also typically quite loud. The advantage is their high production capacity of around 100 liters per hour.

Less common in this category are systems that run on 12V or whose high-pressure pump is driven directly by the main engine.

As a budget option, there are DIY projects available online that use a pressure washer as a high-pressure pump. This significantly reduces the purchase price of the system. Whether the reliability is sufficient for you is up to you. We weren't convinced by this solution – ultimately, due to its performance and noise level.

Systems with energy recovery

New watermakers operate at significantly lower pressures than systems with high-pressure pumps. The former require system pressures of 60 bar, which the pumps must deliver. Systems with energy recovery operate at only 6-8 bar, thus consuming significantly less energy. The pressures required for the membrane are generated by pistons within the device. These systems are usually powered by 12V and, due to their low energy consumption, can easily be powered by batteries. They produce 30 to 60 liters per hour; in exceptional cases, even more.

Which watermaker did we choose and why?

As a mechanical engineer, I was initially skeptical about the new systems. I originally wanted to configure and assemble a modular watermaker myself, using proven components. However, after intensive research and evaluating the systems at the Boot trade fair in Düsseldorf, I changed my mind.

We chose the Schenker Zen 50This runs on 12 V and produces 50 liters of clean drinking water per hour. The system is delivered from the factory with all the necessary components, and in my opinion, the price-performance ratio is very good. Since the Zen 50 has two feed pumps, redundancy is built in. The device works with both pumps as standard, but can also be operated with just one of the two pumps, then delivering half the water production but also using only half the power. You can select whether pump 1, pump 2, or both pumps are running on the control panel.

Another deciding factor was the procurement of parts in the countries we visited. Locally, the parts were usually twice as expensive as realistically necessary. Freight and customs costs would have been a pain if we had ordered online. Only a more American manufacturer would have met our requirements. However, they had decided to stop deliveries outside the US. The reason: a parts shortage due to the supply chain disruptions caused by COVID.

Install it yourself or have it installed?

I decided to install the system myself. Besides the cost savings, the main advantage is that you get to know all the system's components and can intervene at any time if problems arise. Installation is simple and straightforward. You should first consider where each component would be best placed.

Our Zen 50 is from the company Mar Nautic in Switzerland. Maja and Dominique are bluewater sailors themselves. Both were very helpful from the initial contact through delivery and installation. I highly recommend them both.

Which accessories are useful?

When installing a watermaker, you should also consider which additional parts you'll need for operation (see Operation and Maintenance). MarNautic gave me good advice here, too. As a bluewater sailor, you should have the following parts on board:

• Fine filters should be replaced every 100 hours or so. Their lifespan depends heavily on the water quality in which the watermaker is used. Our filter has already lasted more than 100 hours, but we generally operate the watermaker at sea. In bays, there's often a lot of suspended matter in the water that clogs the filters, even if the water appears clear.
  Some crews regularly remove the filters to clean them and dry them in the sun. In my experience, this isn't necessary or even beneficial if the system is operated in clean water.
• Carbon filter, this should be replaced once a year. It's needed to ensure that no chlorine enters the membrane, as chlorine destroys the membrane. Theoretically, you could even do without the carbon filter if the membrane is rinsed exclusively with water from the watermaker.
• In any case, you should have the chemicals on board to be able to preserve the watermaker during longer absences (see sources of error – this can be expensive).
• As always, anything can and will break. So, depending on your gut feeling, choose a good selection of suitable hoses, hose connectors, seals, etc.

Operation and maintenance

We have the device with the simple control panel. Operation is incredibly easy and therefore requires no further explanation (see also Watermaker Installation). It's important to rinse the membrane with fresh water at the end of the production process. This also happens automatically. As long as the watermaker is used again within a week, this is sufficient. The rinsing process can be repeated at any time to extend its service life.

During operation, all you need to do is ensure the filters are clean. The pre-filter can be easily rinsed with water from time to time. Change the fine filter after approximately 100 hours as described above. If there is any air in the system, it should be drained.

If the watermaker is not needed for a longer period of time, the membrane must be preserved with a chemical.

Sources of error – This can be expensive

Watermaker membranes are extremely durable when properly treated; manufacturers claim a lifespan of 10 years. However, it's also easy to quickly render these expensive membranes unusable. The following should be avoided at all costs (this list is not exhaustive):

• The membrane must not come into contact with chlorine, therefore use carbon filters
• The same applies to oil, gasoline and other unknown chemicals, therefore never operate watermakers in ports, marinas, polluted water
• The membrane needs to be preserved when not in use. I would recommend using the manufacturer's chemicals for this. There are all sorts of tips on the internet, though. I think you can't really save money here, or rather, you're saving money on the wrong things.
• The membranes must not dry out, so do not remove the watermaker and leave the membranes open
• If the watermaker comes with built-in membranes, you should check how long the preservation lasts.

BTW: A watermaker should never be left running unattended, even if the controls allow it. If a hose bursts or slips, the amount of water entering the boat can be considerable in a very short time.

Coming Soon: Watermaker installation on Lagoon 421 – don’t miss it!