Watermakers

[SailNet]

Reverse osmosis watermakers have expanded flexibility and safety on board sailboats that wasn’t available to sailors before. Watermakers provide a way to extend cruising range without having to add more tankage or a wish for rainwater. They also provide a safe source of potable water where the water supply may be iffy or perhaps costly. In addition, a large racing crew can be kept adequately hydrated without carrying large quantities of undesirable weight.

REVERSE OSMOSIS—HOW IT WORKS
In the normal process of osmosis, pure water and salt water try to reach a balance when separated by a membrane. The normal flow will be for pure water to seek the salt water because it can pass through the membrane more easily. Reverse osmosis (RO) is the process of applying high pressure to counter the natural osmotic flow, forcing the saltwater through a semi-permeable membrane that permits water molecules to pass through, but not contaminants. RO units not only desalinate, but also reject impurities. They can also act as purifiers by passing the RO water through a filtration unit, which removes over 99 percent of microorganisms, or particles as small as .00019 microns, depending on the unit that is purchased. To put this into perspective, viruses are .004 microns and bacteria are .3 microns.

There are four variables that affect the quantity and quality of RO water.

• Pressure will determine both the quality and quantity of potable water produced. The greater the pressure, the better the quality and the larger the quantity. Units with 60 psi are ideal.
  
• Water Temperature determines the RO system water production. The best temperature is 76 degrees Fahrenheit with 85 degrees an operating maximum. The colder the seawater, the less fresh water is produced. Warmer water fosters bacterial growth
  
• Dissolved Contaminants, or for our purposes, the saltier the intake water, the less RO water is produced unless additional pressure is applied to the system.
  
• Membranes come in a variety of types with different characteristics. Some produce more potable water, some reject more contaminants, and some have longer life because of resistance to contaminant abrasion. The thin film composite (TFC) membrane offers the best features of all three types.

WATER PRODUCTION

• Determine the average daily water usage you desire and purchase a unit that will require running every day, or at least every other day, to produce that amount.
  
• Handheld units from 1 oz / 2 minutes up to 1.5 gallons per hour (gph)
  
• Fixed units 1.2 to seven gph
  
• Larger units from 17 to 63 gph.

TIPS

• Manufacturers recommend operating the watermaker frequently, once a day for several hours rather than once a week, to keep the membrane healthy. Most systems self-clean the membrane with a method called "cross-flow filtration." Some of the fluid in the chamber passes through the membrane while some continues to flow through, washing the rejected contaminants away.
  
• Run the unit in as clean salt water as possible. Oil and other pollutants normally found in harbors will reduce the life of the membrane. A new membrane can cost as much as $450.
  
• Purchase a unit that matches not only your water requirements, but also the capacity of your electrical system. Do you rely on the engine to charge the batteries, on solar power, or on wind generation?
  
• Add prefilters to prevent sand from entering the system and ruining the membrane.
  
• The water intake and discharge of units that make less than five gph are Td off the engine intake and discharged through a hose large enough to take the volume of water.

INSTALLATION
The installation of the unit will require an electrical connection for the pump and numerous plumbing connections. A basic knowledge of electrical and plumbing systems is necessary.

Toolbox

• Electrical wire (size recommended by the equipment manufacturer)
  
• Wire stripper and connectors
  
• Plumbing hose
  
• Ts
  
• Hose clamps
  
• Complete mechanical toolbox

 

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