Watermakers and Potable Water on Private Yachts

Potable water, also known as drinking water is something you might want for long stretches on the water. Water makers onboard create water from salt water. In this article Don will go through the two main types, what to consider and how good the water quality is.

Most vessels in the private yacht industry in Australia will use a reverse osmosis water maker to produce water on-board. Larger vessels that have the space will often use Flash Evaporators.

First, we will explain the difference between the two:

• Reverse osmosis uses high-pressure pump to push sea water through a membrane. This removes the salt and solids to produce fresh water. The next step is to pump fresh water into dedicated desalination or fresh water tanks. Finally in reverse osmosis, the last step is to disperse concentrate (salt/solids) overboard.
• Flash evaporators use a vacuum chamber system and utilise engine heat to extract fresh water from the salt water. As water boils at a lower temperature in a vacuum, engine heat (typically 85°C ) will boil sea water. Evaporators then direct steam into a chamber. The chamber will cool, collect, then pump steam into the fresh water tank. As a result, what remains is a brine solution at the bottom of the vacuum chamber. Lastly, flash evaporation involves circulating brine around and ejecting it 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. Flash evaporators will give you results as low as 0-15ppm.

What does PPM mean and why is this important? 

PPM (parts per million) is the total TDS (total dissolved solid) in the water that you have produced. A lower number indicates better quality potable water. Australian standards will accept water quality up to 500ppm TDS. However, anything up to 1000ppm is acceptable. Where I’m from in Scotland, we like ours lower than 150ppm. 

Will you notice the difference between potable 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. You collect water on a boat through desalination which is not a natural process.  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. As a result, nutrients that are taken out during the desalination process are added back into water.

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.

Potable Water Storage

Storage of potable water is also important. Incorrectly stored potable water can cause bugs infestations. This can lead to legionnaires disease – a lung infection like pneumonia that is dangerous for individuals with underlying health conditions and the elderly.

Poly water tanks are fitted on most modern vessels which 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.

Use it or lose it

Regular use of most onboard systems is critical. For instance, frequently used and replenished water is less stagnant. This will 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.

If you have any other questions or queries related to all things boating, you can contact us here.