Watermakers and Potable Water on Private Yachts

Potable water, also known as drinking water is something you may be interested in if you find yourself on a boat for a long period of time. We often get asked about how to use water makers onboard and how good the quality of water is, and in this article Don will go through the two main types and what to consider.

Most vessels in the private yacht industry in Australia will use what they call a reverse osmosis water maker to produce their water on-board, and some larger vessels will use flash evaporators.

First, we will explain the difference between the two:

  • Reverse osmosis is when a high-pressure pump is used to push sea water through a membrane which removes the salt and solids to produce fresh water. The fresh water is then pumped to a dedicated desalination tank and/or fresh water tank pending the configuration onboard, and the concentrate (salt/solids) is disposed of overboard.
  • Flash evaporators use a vacuum chamber system and utilise heat from your engines to extract the fresh water from the salt water. As water boils at a lower temperature in a vacuum, you can use the engines heat of typically 85°C to boil the sea water, the evaporate/steam created is directed into a chamber to be cooled, collected then pumped into the fresh water tank. This will leave a brine solution at the bottom of the vacuum chamber which can then be circulated around and ejected overboard.

The biggest difference between these two methods is the quality of the water. Reverse osmosis you will typically get a result of 300-400ppm whereas flash evaporators will give you results as low as 0-15ppm.

What does PPM mean and why is this important? 

PPM is the total TDS (total dissolved solid) in the water that you have produced – the lower the number, the better quality the potable water is. Australian standards will accept drinking water quality up to 500ppm TDS and advise that anything up to 1000ppm is acceptable, even though where I’m from in Scotland, we like ours lower than 150ppm. 

Will you notice the difference between water you make onboard and water from your tap at home? 

The answer is yes – the cleaner the water the nicer it tastes. Your tap water has been collected through a natural process, whereas your vessels desalinated water has not. Chemicals in Australian water are also added, which will affect the taste.

One way to make it taste nicer is to add inline filters like carbon or rock filters. These add nutrients back into the water that have been taken out during the desalination process.

Unfortunately, at the time of writing this article there are no flash evaporators currently in production for yachts under 200ft. The downside is they require more room, and more maintenance. The upside is they produce a much better water quality and utilise the engines own byproduct of heat to produce it.

This makes the only viable choice for most of our readers to be reverse osmosis, which is a good option considering the usage and size of most of the vessels around Australia. They are simple to use, easy to maintain whilst still providing you with water of an acceptable drinking quality.

Storage of potable water is also important. If water is stored incorrectly, bugs can form which can lead to legionnaires disease – a lung infection like pneumonia that is dangerous for individuals with underlying health conditions and the elderly.

Most modern vessels will be fitted with a poly water tank as these are safer and generally last longer than the metal alternative. Another advantage of poly tanks is that they can be set up with a self-cleaning system whereas with a metal tank, it’s a requirement to drain the tank to clean it. This means two tanks are needed to allow uninterrupted supply of fresh water onboard, which becomes increasingly important when completing long passages. 

I would suggest to try and use the onboard water as quickly as practically possible and to flush out the tanks every few months to remove any growth that could be festering inside. Another option would be to install an inline UV filter which will kill any bugs as the water passes through it. If you think you will not be using water or are going to leave the boat for an extended period, it would be a good idea to treat the fresh water tanks with chlorine – which is best to have a trained professional perform this task.

Like most onboard systems, it’s all about regular use – the more the water is used and replenished, the less time it has to stand stagnant and cause you problems. Most commonly in Australia we see bottled water onboard for drinking and find the tank water used for showers, washing machines, dishwashers and cleaning. 

If you are planning to use your boat for long periods of time, it would be a good idea to add additional filtration systems as stated above to improve the safety and quality of water onboard. At the same time, you will also be helping the environment by reducing your plastic waste by refilling reusable bottles.

About The Author – Donald Nicholson

Growing up on the Isle of Barra on the West Coast of Scotland (population of around 1100), Don’s family owns and operates a fleet of fishing vessels that mainly fish for prawns and lobsters. At age 17, Don completed a degree in Marine and Mechanical Engineering, and has spent the last decade working in numerous engineering roles across the globe, before settling in Australia in 2017. Don specialised in diesel engines working on a diverse number of vessel and engines across Pittwater. Don has also completed his Diploma in Marine Surveying, and is a valued BoatBuy team member. Liked this article? Feel free to get in contact direct at don@boatbuy.com.au.

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