What output should your watermaker deliver?

Watermakers are available in different performance levels and the question inevitably arises as to which size is the right one for your needs.

Various aspects play a role here and should be considered and weighed up.

  • The water requirement
  • The energy supply
  • Runtime & noise emissions

In the following, the individual points will be discussed and the whole thing will be played through using two examples.

The water consumption

As different as the boats are, so are their users. This is also reflected in the water consumption, which varies extremely from crew to crew.

The easiest way to determine your own consumption is to divide the available tank capacity by the number of days that typically pass until the tanks are empty.

Alternatively, usage behavior can be noted and consumption can be estimated. We will explore this theoretically using two examples.

Indications for consumption per person:

  • Drinking water 3 l
  • Personal hygiene 2 - 20 l
  • Laundry: 7 l (assuming 1 load per person per week)
  • Dishwashing: 0.5 -5 l

Obviously the biggest influence is comfort - is there a washing machine on board and how much do you shower with fresh water?

A consumption of just 5 L / person and day can be just as realistic as 40 L / person and day.

With all these considerations, one thing should be taken into account: It is certainly easy to limit your water consumption to a minimum for the weeks of an ocean passage. However, whether you want to implement this permanently for the times at anchor is a different question that everyone has to answer for themselves.

With the convenience of a watermaker, water will become a less scarce commodity on board and many crews will accordingly see an increase in water consumption. So it's better to allow for a certain safety margin.

We choose two examples for further consideration:

Aneconomical two-person crew using 15 l / day.

The comfort oriented crew that might have guests on board - 100 l/ day.

The energy supply

In addition to the efficiency of the Watermaker, how much energy is available determines the amount of water that can be produced. Another aspect is the question of how the energy is generated and stored and whether this may impose any restrictions on the running time of the Watermaker.

Basically it can be said that a watermaker with energy recovery consumes around 4-4.5 Wh/liter of energy based on the amount of water produced. For a conventional watermaker, this consumption is in the order of 6.5 - 12 Wh / liter depending on the configuration (membranes) and water temperatures - we assume 8 Wh / l in below examples.

The efficiency does not take into account the amount of fresh water that is used again to flush the system after operation has ended. If the Watermaker is not used every day, but produces more water with each run, this becomes less and less important.

Let's take our examples:

  • The economical two-person crew comes to 60-120 Wh/day at 15 L/day, depending on the type of watermaker.
    • This corresponds to 5 - 10 Ah / day at 12 V of energy consumption for water needs.
  • The bigger crew consumes 400-800 Wh/day of energy at 100 L/day
    • So 33 or 66 Ah / day at 12 V

For comparison: The refrigerator compartment on board a standard 40ft yacht typically uses around 50-60 Ah per day at 12V.

Conclusion: The most effective way to save energy is through water consumption. The needs of an economical crew can be met even without energy recovery with negligible power consumption. Energy recovery has a non-negligible effect, but even with a conventional watermaker, most boats can easily meet a comfortable water requirement.

Runtime and noise level

In addition to pure water consumption and energy requirements, another aspect when sizing the Watermaker is the running time and the noise level during operation.

For example, if you have a small battery bank and excess solar that you want to use, you might want to consider a small, efficient unit that runs regularly over longer periods of time to use the excess without putting too much strain on the battery.

In such a case, we recommend a small energy-saving unit, such as the Aqua-Nautica AN-25.

If there is a large lithium battery bank or even a generator available that runs regularly anyway, the considerations are completely different.

With a generator on board, you usually want to produce as much water as possible during its running time in order to utilize its power. A conventional, modular watermaker is ideal here.

With a large battery bank there is no "time pressure", but higher performance can be used and the Watermaker's short running time can cover the water requirements without having too much of an impact on life on board with the noise of the Watermaker.

Here again are the examples above:

The economical crew has a small battery bank and some solar surplus. The Watermaker runs every third day to cover 45 liters of water consumption. In order to be able to flush the system, another 5-10L extra must be produced.

The less economical crew with 100 l / day wants to fill their tanks every 5 days. A unit that produces 180 l/hour and also requires around 10 l of water for flushing will have to run for about 3 hours.

In the examples above, a look at the operating times shows that the Units fit the respective needs very well. The noise pollution is limited to a few hours every few days and the operating hours accumulated annually make the units smile tiredly - the best prerequisite for long, worry-free operation.