Watermaker Explained

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".

The devices can be expensive to acquire and maintain, but are quite valuable because they reduce the need for large water tanks for a long passage.

The term watermaker may also refer to an atmospheric water generator, a machine that extracts potable water from the humidity in air using a refrigeration or a desiccant.

Varieties

Many versions are used by long-distance ocean cruisers.

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.

Water requirement

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.[1] 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 amount of water that is required for a person to consume is dependent on different factors. Some of these factors include weight, height and gender. Men on average needs a greater amount of water than women do.[2]

Popular brands of yacht watermakers typically make from 2 to 150 litres per hour of operation (0.53 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:

Pros

Cons

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.

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 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.

An innovation in the desalination technology was registered in the United States by Schenker Watermakers. According to the US Patent,[3] it is an Energy Recovery System, which allows to activate the reverse osmosis process, obtaining an energy savings of approximately 80%. This technology does not require the use of high-pressure pumps even for the sea water desalination, and therefore allows to greatly reduce the consumption of electricity. The technology is available for flow rates up to 500 lit/h of fresh water produced.

Atmospheric water generator

See main article: Atmospheric water generator. An atmospheric water generator is a machine that extracts potable water from the humidity in air using a refrigeration or a desiccant. Condensing moisture by refrigeration requires a minimum ambient temperature of about 10C15C, while desiccant adsorbers have no such restriction. Either method is suitable for a desert climate, where water production is dependent on ambient humidity. The Negev desert in Israel, for example, has a significant average relative humidity of 64%.[4]

Contrary to some online sources,[5] a 1922 article in Popular Science cites an average relative humidity of 30% for the Sahara Desert, about half the humidity in an air-conditioned home.[6] Moreover, the effect of the dew point causes early mornings to have higher humidity, so that atmospheric water generation is possible even in the harshest climates.

Notes and References

  1. http://www.vdh.virginia.gov/DrinkingWater/documents/waterconservation/appendib.pdf Virginia GPCD
  2. Web site: Plain Water, the Healthier Choice. CDC. 2018-10-23. Centers for Disease Control and Prevention. en-us. 2019-04-26.
  3. USPTO. Patent n. 6,491,813 B2, United States Patent and Trademark Office, 2002-12-10.
  4. Web site: Drinking Water from Air Humidity. Science Daily. 4 January 2012.
  5. Web site: Sahara. The Free Dictionary. 4 January 2012.
  6. Driscoll. W. H.. How You Can Burn 30% Less Coal and Still Keep Warm This Winter. Popular Science Monthly. 1922. 101. 32. 4 January 2012.