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".

Varieties

Many different versions are frequently 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 also converts to hand operation in an emergency.

Water requirement

There is great variation in the amount of water consumed per day. At home in the United States, each person uses 140 liters of water per day on averageFact|date=May 2007. Where supplies are limited, and in emergencies, much less may be used.

Typical cruising yachts use from 4 to 20 liters per person per day, the average probably being about 6 liters. The minimum water intake required to maintain body hydration is 1.5 liters per day. The maintenance of comfort under normal circumstances requires 3% of mass body weight or typically about 2.3 liters per person of drinking water per day.Fact|date=April 2007

The popular brands of yacht watermakers typically make from 2 to 150 liters per hour of operation depending on the model.

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

Pros

* The user is independent of shore-based water supplies, which is especially important in remote parts of the world.
* They provide safe water when shore-based water is of uncertain quality.
* Some designs are portable and can be converted to manual operation in an emergency.
* The hand-held unit offered by one manufacturer and the towed water-powered watermaker offered by another manufacturer can be transferred to a liferaft in an emergency.

Cons

* They are expensive: indicative costs are US$2,000 for the manual type, US$3,000 for the towed water-powered type, US$4,000 or more for an engine-driven type, designed to be fitted to the inboard motor of the vessel, and about the same for an AC generator-driven type.
* Some types (but not all) are time-consuming and expensive to maintain.
* They are very power hungry, except the hand-held emergency watermaker and the towed water powered type. Accordingly, these devices overcome the problem of large electric current demand. The drawbacks for these non-electric designs are that manual operation is tiring for the operator and the towed watermaker only works while the vessel is moving through the water.

Some manufacturers of electrically powered watermakers have energy recovery systems incorporated in their designs 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 power consumption from perhaps typically 20A to about 8A.
* Like every additional piece of equipment, it is bound to fail at some time in the future and cause expense/anxiety.

Technology

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 which 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 68 bar are required, the process is much more complex than the common water filter or the oil filter found in our automobile engines.

Atmospheric water generator

Another type of watermaker available is the atmospheric water generator, a machine that makes pure drinking water from the air by refrigeration. These are, however not energy efficient in comparison to reverse osmosis technology. Their great advantage is there is no water supply required as they obtain the water from the atmosphere. The drawback is that they require moist air to function and the output is relatively very small.