PS Advisor: 08/15/05

Watermakers and Toxins
I was in the process of buying a Little Wonder watermaker when a fellow sailor in my marina questioned the wisdom of watermakers on sailboats. Specifically, his concern was bottom paint toxins going into the saltwater intake.

Often the bottom paint we sailors apply is as toxic as possible given governmental restrictions. In many parts of the world, said this sailor, the toxicity of bottom paint one can purchase is extreme. On his boat, the intake, prior to getting rid of his watermaker (a PUR), was aft and this allowed sloughed paint along the entire boat's length the opportunity to be taken into his system. Reverse osmosis can get rid of a lot of things, he contends, but not PCBs and other carcinogens. Would one really want to drink/cook with tainted water given such a prospect?

Can you set me straight on this issue?

Rick Gaines
Friday Harbor, WA

There is no really simple answer to this question. Because the reverse osmosis process removes only a percentage of total dissolved solids in the feedwater, there could always be traces of potentially hazardous chemicals in potable water produced by a boat’s reverse osmosis watermaker. For example, reverse osmosis will typically remove over 98% of arsenic, but only 80% of selenium. Depending on the concentration of these materials in the feedwater, you may be left with trace amounts of hazardous materials, or significant amounts.

Modern antifouling paints use a variety of biotoxins, as well as several different delivery systems for them. As a rule, however, there is not normally a cloud of polluted chemical soup generated by your bottom paint hanging around the outside of your hull waiting to be sucked into the feedwater intake. Having said that, you should also use common sense when operating a watermaker.

We would not run the watermaker while cleaning the bottom, or within several hours of cleaning the bottom in an anchorage that is not tidally flushed. In an anchorage, we never run the watermaker in the morning, when other boats are most likely to flush toilets into the water.

Whenever possible, we do not run the watermaker in anchorages that are shared with large numbers of commercial vessels or yachts, such as the Flats anchorage at the Caribbean end of the Panama Canal. We also have the habit of anchoring well offshore and away from other boats when it is practical, if we plan on making water.

As a final layer of protection, we have an under-counter carbon filter at the galley sink for all water used for drinking and cooking. A high-quality carbon-matrix filter such as General Ecology's Seagull IV will remove a very large number of potentially hazardous substances and organisms from your drinking water. Whether you have a watermaker or not, carbon filtration of water used for drinking and cooking is a good idea on a cruising boat.

Frankly, even with the risk of chemical contamination in the feedwater supply, you may well be better off drinking water you make than water that comes out of the tap ashore. In many parts of the world, there is little or no treatment of tapwater, which may contain biological and chemical contaminants. Even in the U.S., groundwater in many areas is contaminated with more hazardous chemicals than you typically find in mid-ocean seawater.

There are many parts of the world where even the locals do not drink the water that comes out of the tap. Even if they do, that's no indication that the water you might put into your tanks via a hose at a dock would be considered safe to drink by U.S. standards.

Until you go cruising to areas like Southeast Asia and Africa, you don't realize just how spoiled we are in the U.S., where we assume that the water that comes out of any tap is suitable for drinking. Safe drinking water is a luxury in many parts of the world.

A watermaker gives the cruising boat an enormous amount of freedom. When former editor Nick Nicholson circumnavigated aboard Calypso from 1997 to 2002, he made over 7,500 gallons of potable water with his Little Wonder watermaker. He sometimes pumped water from his tanks into other boats without watermakers when they couldn't find local sources of drinking water.

Whatever risk there may be from running chemically contaminated seawater through your watermaker, we think it can be minimized through the use of common sense-and a good carbon final filtration system.

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