Water Quality 101

There are three common types of water quality improving methods found on yachts, and each has its place and purpose:

  • ‘Filtration’, such as a Sediment and Charcoal Filters.
  • ‘Purification’, such as a Reverse Osmosis System.
  • ‘Sterilization’, such as a UV light or a Silver Sterilizer.

Filtration: Most yachts use Sediment Filters or Charcoal (Carbon) filters. Sediment filters remove suspended solids (down to the micron rating of the filter), and Charcoal filters remove unpleasant tastes and odors that water may have acquired from being stored or from the vessel’s plumbing system. Charcoal filtration also reduces chlorine and other disinfectants that may have been added to the water supply.

Purification: The most common type of purification used on yachts is Reverse Osmosis (RO). Unlike filtration, RO will remove a significant amount of dissolved solids, such as salt (sodium chloride) and hardness such as calcium and magnesium. A sea water RO system is used to desalinate sea water while the vessel is offshore or at anchor, and a fresh water RO system is used to purify dock water while the boat is at a dock . Fresh water RO will bring product water to less than 20 parts per million (ppm) of TDS, eliminating the need for hand drying vessels after wash downs and remove 99.5% of total dissolved solids, bacteria, cysts, viruses, and radioactive contaminants from feed water.

Sterilization: Once water is free from dissolved solids, sterilizers ensure that water remains potable, free of biological contaminants, after it is produced and stored. UV sterilization is most effective when installed post-tank and immediately before the water is distributed to the boat’s fresh water system. UV lights are sized by how many gallons per minute they can sterilize. The boat’s maximum fresh water pumping volume should determine the UV light size.

If a boat is a class-rated vessel, a ‘Residual’ method of sterilization may be required. The two common types are Chlorine injection and Silver Sterilization. Silver Sterilization sterilizes through controlled electrolysis between two silver plates, and is preferred since it only adds less than 1 part per million (ppm) of silver to the water. A Chlorine injection approach requires storage of chlorine onboard and then injecting it into the water in a controlled manner, not a preferred approach.

The Ideal Setup: Ensure that all water going into the boat’s fresh water storage tank, whether sea or shore water, is first purified with Reverse Osmosis. A sediment filter followed by a carbon filter should be employed after the storage tank and downstream of the fresh water pump before distribution to the boat. This will ensure removal of suspended solids, as well as taste, and odor acquired from the storage tank or plumbing. Finally, a sterilization method, such as UV light or Silver Sterilizer, should be used for biological purity.

Summary: With the proper application of filtration, purification, and sterilization, a vessel’s onboard water supply will be suitable for any use, including human consumption. These steps can greatly improve a crew’s ability to maintain a boat in addition to eliminating the need to purchase, store and consume seemingly endless cases of bottled water.


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