Decontaminating a Tainted Water Tank

Posted by Darrell Nicholson with Drew Frye at 03:23PM - Comments: (26)

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.

Where's all that gunk coming from? Here's what one of our test pre-filter looked like after just 50 gallons from a dockside hose.

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.

Comments (26)

Has anyone used the Puriclean alternative to bleach?

Posted by: Geeners6 | September 24, 2018 10:21 PM    Report this comment

Are there any issues with leaving the chlorine (bleach) solution in the system for 48 hours or more hours instead of the 4 hours recommended in the procedures above? I'm asking because of a timing issue of when I can get this done. Thanks!

Posted by: rsqunit | August 5, 2018 9:20 PM    Report this comment

The bleach calculations and wording are from ANSI standard A119.2 section 10.8 and are based on household 5% hypochlorite bleach. The hydrogen peroxide calculation is based on a 3% drug store solution.

The weaknesses of UV light treatment are that is does reach the plumbing, is hard on plastic tanks, and requires frequent cleaning of the lamps. Although it can be effective for in-line sterilization with proper pre-filtration and lamp maintenance, it is not recommended for storage tanks.

Hydrogen peroxide can be a sterilizing agent, but only if mixed from stronger concentrations (it needs to be 3% in solution to be effective). These stronger solutions (one poster mentioned 50% HP) are quite hazardous to handle and are not recommended for DIY use. There are no protocoles for using hydrogen peroxide to treat drinking water; if used in high enough concentration to be effective, it is unhealthy to drink. Thus, drinking water sanitation protocoles are based on bleach.

Posted by: Drew Frye | July 22, 2018 7:36 AM    Report this comment

Is Step 2 really "multiply by 1.0?" What's the point?

Posted by: James | July 20, 2018 8:17 AM    Report this comment

Really useful article. Very grateful if someone could clarify 2 points of detail, the article states "If the smell of bleach persists after two refill and drain cycles, add a teaspoon of hydrogen peroxide per 20 gallons and mix". Hydrogen peroxide seems to be readily available in various solution strengths of between 3% and 12% -does anyone know what hydrogen peroxide solution strength the "a teaspoon of hydrogen peroxide per 20 gallons" based on?
Also, I presume the solution strength (out of the bottle) of the household bleach referred to in the article is 5% -again, grateful if anyone can anyone clarify since sodium hypochlorite (bleach) is available in solution strengths of up to 12% (for swimming pool disinfection)

Posted by: David Strong | July 20, 2018 6:05 AM    Report this comment

To sterilize water you need either chemicals or energy. Personally I prefer to use energy. Once the tank is clean it needs to be a hostile environment for algae, slime and bacteria or you will be cleaning again while the boat is sick from foul water.

Use UV LED's inside the tank and in inline UV sterilizer to the faucets. UV can also sterilize diesel fuel tank as well. UV will reduce the load placed on your fuel polisher as well. You can even use UV to sterilize your blackwater.

A 10 watt led is very efficient and generates extremely little or no heat. You do not need to keep it on continuously but it can strobe and the line sterilizer only needs to be on while water is flowing.

www dot ecnmag.com/blog/2014/04/understanding-ultraviolet-led-applications-and-precautions

eponline dot com/articles/2016/04/28/how-leds-will-change-water-purification.aspx

www dot dfs.semanticscholar.org/ba9c/0a0d92682644a50287593b1536b7d0289750.pdf

Posted by: rav555 | July 12, 2018 10:38 AM    Report this comment

To sterilize water you need either chemicals or energy. Personally I prefer to use energy. Once the tank is clean it needs to be a hostile environment for algae, slime and bacteria or you will be cleaning again while the boat is sick from foul water.

Use UV LED's inside the tank and in inline UV sterilizer to the faucets. UV can also sterilize diesel fuel tank as well. UV will reduce the load placed on your fuel polisher as well. You can even use UV to sterilize your blackwater.

A 10 watt led is very efficient and generates extremely little or no heat. You do not need to keep it on continuously but it can strobe and the line sterilizer only needs to be on while water is flowing.

www dot ecnmag.com/blog/2014/04/understanding-ultraviolet-led-applications-and-precautions

eponline dot com/articles/2016/04/28/how-leds-will-change-water-purification.aspx

www dot dfs.semanticscholar.org/ba9c/0a0d92682644a50287593b1536b7d0289750.pdf

Posted by: rav555 | July 12, 2018 10:38 AM    Report this comment

As the old saying goes, if momma ain't happy, ain't nobody happy.

In my book, prevention is the best approach. Said another way: PPPP -- prior preparation prevents problems.

A few years ago after my fiberglass water tank turned into a petri dish of horrors over the winter and added a full day to my springtime commissisoning, I changed my winterizing procedures from wet to dry. No more propylene glycol (AKA pink stuff) in my water system!

Instead, I ran all water out of the tank using the onboard domestic water pump and its backup, then vacuumed out the small amount left in the bottom of the tank using a shop vac. There was no sign of algae or contamination, so it was not necessary to scrub the tank. I also drained the hot water heater. Then I turned the shop vac around and used its high volume/low pressure (with all faucets open) to blow the remaining water out of the water lines (hot and cold), one by one. While there was a little moisture left in the system, it wasn't enough to freeze solid and expand and damage the plumbing. When I return to the boat in the spring, I just fill the water, prime the pumps, and run the air out of the system, and we're good to go--no pink stuff to try to get rid of, no chemistry experiments, no bad taste, no bad smells. Easy-peasy. And it keeps the admiral very happy.

One side note: I do use the pink stuff to winterize my Village Marine Tec watermaker, and that has the blessing of Village Marine. They tell me it's much less harmful to watermakers, including the membranes, than the caustic chemicals usually used in to clean watermakers, and, of course, it won't freeze. It's worked perfectly over the past five winters, and the watermaker always comes right back online once the pink stuff is pumped out.

Posted by: Milt Baker | July 12, 2018 9:55 AM    Report this comment

I'm wondering if anyone has used products like Five Star or Star-San ? I use these products in my beer making process. Choline can be used in the cleaning process, but there are better and safer products available to clean hoses, plastic containers and metal. I don't know if you can compare cleaning sealife to yeast, but they are both living organisms. I look at the plumbing of my boat and it's made of the same materials as my brewing equipment. I would say that it is not cheaper then iodine, but it leaves no off taste or odors and keeps my brewing equipment fresh and clean.

I see that this article was written 2015. I hope it's appropriate to add this comment now.

Posted by: Cmccrew | April 16, 2017 1:24 PM    Report this comment

I'm wondering if anyone has used products like Five Star or Star-San ? I use these products in my beer making process. Choline can be used in the cleaning process, but there are better and safer products available to clean hoses, plastic containers and metal. I don't know if you can compare cleaning sealife to yeast, but they are both living organisms. I look at the plumbing of my boat and it's made of the same materials as my brewing equipment. I would say that it is not cheaper then iodine, but it leaves no off taste or odors and keeps my brewing equipment fresh and clean.

I see that this article was written 2015. I hope it's appropriate to add this comment now.

Posted by: Cmccrew | April 16, 2017 1:24 PM    Report this comment

I'm wondering if anyone has used products like Five Star or Star-San ? I use these products in my beer making process. Choline can be used in the cleaning process, but there are better and safer products available to clean hoses, plastic containers and metal. I don't know if you can compare cleaning sealife to yeast, but they are both living organisms. I look at the plumbing of my boat and it's made of the same materials as my brewing equipment. I would say that it is not cheaper then iodine, but it leaves no off taste or odors and keeps my brewing equipment fresh and clean.

I see that this article was written 2015. I hope it's appropriate to add this comment now.

Posted by: Cmccrew | April 16, 2017 1:24 PM    Report this comment

Comments about Hydtogen Peroxide are wrong. You do not need gloves to handle it. It's fumes are not dangerous. You can use Hydrogen Peroxide as a mouth wash, to clean your ears, to clean dirty wounds, to lightly bleach hair and teeth. It's an excellent product to keep in any home medical kit.

Posted by: Rweinc | April 16, 2017 10:27 AM    Report this comment

Comments about Hydtogen Peroxide are wrong. You do not need gloves to handle it. It's fumes are not dangerous. You can use Hydrogen Peroxide as a mouth wash, to clean your ears, to clean dirty wounds, to lightly bleach hair and teeth. It's an excellent product to keep in any home medical kit.

Posted by: Rweinc | April 16, 2017 10:27 AM    Report this comment

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.

I am noting the the dilution in case 1. is 1280:1 and that in case 2. is 1000:1--close enough, I assume.

Posted by: Cody | April 11, 2017 10:23 AM    Report this comment

@sailing Jack, iodine sanitizers should be fine for this application, but as with any sanitizer, follow label directions for dilution carefully. I also prefer iodine to bleach, and it is just as effective in killing microorganisms.

The key part of any sanitation strategy is that the surfaces must be cleaned before they can be sanitized.

Posted by: bplipschitz | April 9, 2017 10:05 PM    Report this comment

In the dairy industry iodine sanitizers are use commonly. I used to use them for general sanitizing as I preferred the smell and taste. Anyone tried these on boats?

Posted by: sailing Jack | April 9, 2017 6:29 PM    Report this comment

In the dairy industry iodine sanitizers are use commonly. I used to use them for general sanitizing as I preferred the smell and taste. Anyone tried these on boats?

Posted by: sailing Jack | April 9, 2017 6:28 PM    Report this comment

The bleach concentration given was for 4 hour contact time, with an option of increasing the concentration for a shorter time. ANSI does not recognize lower concentrations.

This amount of bleach will be very quickly oxidized to chloride and should pose no hazard to the environment. If you would like to neutralize the bleach before discharge, add an equal amount of hydrogen peroxide (3%), mix, and allow to react for 1 hour. This will oxidize the bleach to chloride, as described in the article.

Posted by: Drew Frye | June 1, 2015 6:35 AM    Report this comment

Can we reduce the chlorine concentration and increase the time in the tank? What level of chlorine concentration is safe to discharge into the water?

Posted by: mcmoorman@hotmail.com | May 31, 2015 7:18 PM    Report this comment

I clean my tanks using 2 liters of 50% Hydrogen Peroxide solution in a 500 liter tank added via a unused vent line during a very slow fill. Bypass all filters and run thru the system doing everything else the author says. Note that one needs gloves to handle to Hydrogen Peroxide as well as eye protections and DEFINITELY do not sniff. After letting it sit for an hour, run thru each water outlet catting the water in some panty hose. If minimal, then continue to run to less than 1/4 tank level and refill. Good to go for another season.

Posted by: LeeZe | May 30, 2015 1:33 AM    Report this comment

The following text was inadvertantly omitted from the original (it is in there now): 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.

Posted by: sailordn | May 28, 2015 11:52 AM    Report this comment

a. Effective tap filtration will remove all of the chlorine anyway (August issue--there are some very good, very cheap filters in the review).

b. It is common to over-chlorinate during sanitation in the mistaken belief that more is better; because high bleach concentrations increase the pH and decrease chlorine reactivity, they can actually reduce sanitizing effectiveness. WHO and EPA have studied this--use only the recommended dose.

c. For seasonal sailors there is an even better answer; clean, empty and DRY the tanks each fall. You wouldn't put the dishes away dirty, would you? A dry tank will be fresh and ready to fill in the spring with only normal (tap) chlorine doseage. Glycol does NOT go in the tank EVER, only in the lines (July issue).

Posted by: Drew Frye | May 27, 2015 5:12 PM    Report this comment

We follow this sequence every year, regularly change out our dockside filter (6 months) and our tap filter (3 months) for drinking water. Taking the time to ensure healthy drinking water in our tanks means no more hauling large water containers on trips or long weekends. I've never tried the vinegar and I've read mixed reviews as to the vitamin C tablet working, although I don't see the harm in trying. If we use the right amount of chlorine in combination with our filters, we do not have any residual chlorine taste or odors, even though I leave the chlorine mixture in my tanks for up to a week.

Posted by: Justin N | May 27, 2015 12:50 PM    Report this comment

what will this amount of flushing do to our fresh water pumps, this is hundreds of gallons of water.

Posted by: Danw@dwinchester.com | May 27, 2015 11:38 AM    Report this comment

Vinegar offers no special magic; any organic material will give the bleach something to oxidize and remove the smell and taste... which coincidentally is exactly how carbon filters remove chlorine. The chlorine burns the carbon, along with any organic material that has been adsorbed onto the carbon. A piece of a vitamin C tablet is often suggested for campers using bleach to sterilize water; it works because ascorbic acid is an antioxidant and is easily oxidized by the bleach.

Posted by: Drew Frye | May 27, 2015 12:17 AM    Report this comment

After refilling and purging until the bleach odor is gone - repeat the whole procedure using white vinegar in place of bleach (same proportions), then drain, refill and purge once more until the vinegar odor is gone. Otherwise you will taste the bleach even though you can't smell it. Reinstall your filters and aerators and then you should be good to go.

Posted by: djblackwood | May 26, 2015 3:08 PM    Report this comment

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