Decontaminating a Tainted Water Tank


Those of you who missed our report on how a weak winterizing solution can create a Sandals Beach Resort for waterborne bacteria may be noticing a pungent odor coming from your galley tap. Regardless of the cause of your water woes, our favorite chemist-sailor Drew Frye has spent most of the winter coming up with some simple steps to ensuring you have fresh-tasting water as good as any bottled variety on board this spring. Here he offers a step-by-step guide to decontaminating that foul-smelling tank.

With careful monitoring and pre-filtering of dockside water and maintenance of tank water, this procedure should only be required when contamination is suspected, or to start off fresh with a clean tank. Regular inspections, filtration at the dock, and maintenance doses of chlorine or treatment tablets (which we will compare in Part II of this series) when needed will prevent future problems. Using a proper mix of glycol if you winterize will prevent one of the common causes of contamination.

First the tank needs to be clean. Look inside with a flashlight; is there any sediment on the bottom or scum on the walls? Feel the walls; are they slick, evidence of healthy bacterial growth? It all must go. Hopefully there is reasonable access, for there is no substitute for a good hand scrubbing and rinse-down with a high powered hose. Machine dishwasher detergent works well as do long handled brushes. A power washer can help, but some angle fittings will be needed and it won’t do the job by itself. Once you’ve taken care of any growth, the next step is sanitizing.

There is a standard sanitizing procedure for recreational vehicles (ANSI A119.2 section 10.8) that works just as well for boats. We’ve added a few details, but the bones of it come straight from the code and have been reviewed and accepted by the U.S. Public Health Service.

  • Turn off the hot water heater until finished.
  • Remove any carbon canisters or micron rated filters. Remove any faucet aerator screens. Wire mesh pump protection strainers should stay in place. The plumbing will very likely slough off a layer of bacteria during later flushing steps.
  • Clean and remove the vent screen and flush the vent hose.
  • Use either following methods to determine the amount of common household bleach needed to sanitize the tank.
  1. Multiply gallons of tank capacity by 0.13; the result is the ounces of bleach needed to sanitize the tank. This is 1/8 cup of plain bleach (no fragrance) per 10 gallons.
  2. Multiply liters of tank capacity by 1.0; the result is the milliliters of bleach needed to sanitize the tank.
  • Mix the proper amount of bleach within a 1-gallon container of water. This will provide better mixing and reduce spot corrosion of aluminum tanks.
  • Pour the solution (water/bleach) into the tank and fill the tank with potable water.
  • If possible, allow some solution to escape though the vent. (If the vent is exterior, prevent any spillage into local waters.) This will sanitize the vent line.
  • Open all faucets (hot and cold) allowing the water to run until all air is purged and the distinct odor of chlorine is detected. Leave the pressure pump on.
  • The standard solution must have four hours of contact time to disinfect completely. Doubling the solution concentration reduces the contact time to one hour.
  • When the contact time is completed, drain the tank. Refill with potable water and purge the plumbing of all sanitizing solution. Repeat until bleach is no longer detectable.
  • If the smell of bleach persists after two refill and drain cycles, add a teaspoon of hydrogen peroxide per 20 gallons and mix. The peroxide will oxidize the hypochlorite to chloride (salt) and oxygen, neutralizing the bleach. Any excess peroxide will be harmless to drink and will have no taste. Peroxides are common ingredients in commercially available water freshening preparations like those we tested. Don’t use vinegar, which can ferment, undoing all of your hard work.
  • Replace all filters and the vent screen.
  • Note for aluminum tanks: Some sailors are afraid of using bleach in aluminum tanks for fear of rapid corrosion. This shouldn’t be a concern for infrequent cleaning when the recommended dosage and time is observed. As an alternative, we found PuriClean to be an effective sanitizer, and it was non-corrosive toward aluminum.

Part One of Frye’s three-part series on onboard water quality, a test of water tank pre-filters, began in the June 2015 issue; the July 2015 issue focuses on keeping water clean and fresh; look for part three in the August 2015 issue. You can follow Frye’s other experiments and sailing adventures at Sail Delmarva.

Darrell Nicholson, editor of Practical Sailor, grew up boating on Miami’s Biscayne Bay on everything from prams to Morgan ketches. Two years out of Emory University, after a brief stint as a sportswriter, he set out from Miami aboard a 60-year-old wooden William Atkin ketch named Tosca. For 10 years, he and writer-photographer Theresa Gibbons explored the Caribbean, crossed the Pacific, and cruised Southeast Asia aboard Tosca, working along the way as journalists and documenting their adventures for various travel and sailing publications, including Cruising World, Sail, Sailing, Cruising Helmsman, and Sailing World. Upon his return to land life, Darrell became the associate editor, then senior editor at Cruising World magazine, where he worked for five years. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.Drew Frye, Practical Sailor’s technical editor, has used his background in chemistry and engineering to help guide Practical Sailor toward some of the most important topics covered during the past 10 years. His in-depth reporting on everything from anchors to safety tethers to fuel additives have netted multiple awards from Boating Writers International. With more than three decades of experience as a refinery engineer and a sailor, he has a knack for discovering money-saving “home-brew” products or “hacks” that make boating affordable for almost anyone. He has conducted dozens of tests for Practical Sailor and published over 200 articles on sailing equipment. His rigorous testing has prompted the improvement and introduction of several marine products that might not exist without his input. His book “Rigging Modern Anchors” has won wide praise for introducing the use of modern materials and novel techniques to solve an array of anchoring challenges.



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