Watermaker

A watermaker is a device used to obtain potable water by reverse osmosis of seawater. In boating and yachting circles, desalinators are often referred to as "watermakers".

Many versions are used by long-distance ocean cruisers. The devices can be expensive to buy and maintain, but are a huge advantage because of the reduced need to have large water tanks for a long passage.

Depending on the design, watermakers can be powered by electricity from the battery bank, an engine, an AC generator or hand operated. There is a portable, towed, water-powered watermaker available which converts to hand operation in an emergency.

There is great variation in the amount of water consumed.

At home in the United States, each person uses about 55 gallons (208 liters) of water per day on average. Where supplies are limited, and in emergencies, much less may be used.

Typical cruising yachts use from 4 to 20 litres (1.05 to 5.28 gallons) per person per day, the average probably being about 6 litres (1.59 gallons). The minimum water intake required to maintain body hydration is 1.5 litres (0.4 gallons) per day. The maintenance of comfort under normal circumstances requires 3% of mass body weight or typically about 2.3 litres (.61 gallons) per person of drinking water per day.

Popular brands of yacht watermakers typically make from 2 to 150 litres per hour of operation (.53 to 41 gallons) depending on the model.

There are strong opinions among small boat cruisers about the usefulness of these devices. The arguments may be summarised as:

Some manufacturers of electrically powered watermakers have energy recovery systems in their design which reduce the power consumption; however, these are typically some 50% more expensive for any similar size due to their additional complexity. As a guideline, assuming a 12V DC system, the energy recovery incorporated in those watermakers have the effect of reducing the electric current used from perhaps typically 20A to about 8A. Like any piece of equipment, it is bound to fail at some time and cause expense/anxiety.

All watermakers designed for small boats and yachts rely on essentially the same technology, exploiting the principle of "reverse osmosis": a high pressure pump forcing seawater through a membrane that allows water but not salt to pass.

The common comparison is that of a filter; however, as the holes in the membrane are smaller than molecules of sodium chloride (salt) and indeed smaller than bacteria, and pressures in the nature of 45-50 bar are required, the process is much more complex than the common water filter or the oil filter found in automobile engines.

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Wikipedia