What is a Watermaker?

What is a watermaker, and what are they designed to do?

A yacht watermaker is a piece of machinery that, through a process of reverse osmosis, turns seawater into drinking water. There are two types:

• Traditional high-pressure watermakers that use a CAT pump to get the required 56 BAR of pressure needed to push the water through the membrane. 
• Energy recovery watermakers. They use a low-pressure pump and hydraulics to get the required 56 BAR, and as the name suggests, ‘recover’ some of the energy expended in getting the 56 BAR of pressure.

What power do you need to power a watermaker?

High-pressure watermakers

Traditional CAT pump-based watermakers normally need AC power in the form of a generator to get the required energy needed to make water. They can be DC powered, but are very energy hungry and more often than not, require the vessel’s engine to be running at the same time that the watermaker is running. 

Energy recovery watermakers

Energy recovery watermakers use low-pressure pumps that bring the seawater into the watermaker at low pressure, typically between 6 to 8 BAR. 

Inside the watermaker, the pressure is increased tenfold. The wastewater brine discharge, whilst still ‘energised’, is redirected via a double piston to ‘recock’ the watemaker by completing the cycle. 

These watermakers are designed to be run from the vessel’s batteries, which can be charged via solar panels, wind and water generators, a generator or the vessel’s engine. Typically, the power draw of an energy recovery watermaker is a fifth of that of a traditional CAT pump-based watermaker.

Advice for choosing a watermaker

How much water do I need?

The Atlantic Crossing Guide says 2.5 litres per person per day x 50% more than the expected passage time. 

This is for very basic needs. Additional requirements for showers, washing clothes etc are not included. 

What a watermaker onboard does, is to change the way that the vessel’s water is used. No need to ration as every day the tanks can be topped up.

Larger vessel owners with generators running 24/7 to power freezers, icemakers etc may opt for a traditional CAT pump-based system. Smaller yachts and sailing vessel owners, where power usage is more critical, tend to opt for the DC-powered energy recovery systems.

For an Atlantic crossing with a crew of four, one of the smaller 30 to 50 litre an hour systems may be sufficient. However, if the vessel is fitted with fresh water flushing toilets and a washing machine and or dishwasher, it will probably need a minimum capacity of 100 litres an hour.

Installation

Space is often an issue. Some of the traditional CAT pump-based systems are quite modular and can be installed around the vessel. The DC-powered energy recovery systems tend to be comprised of a low-pressure pump or pumps with the watermaker part of the system in one piece. 

Installation is critical for both types of system and thought should be given to the location of the seawater intake and the location of the pumps.