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Old 11-12-2018, 15:12   #1
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Sanitizing Fresh Water Tanks

Any recommendations on regular (or semi-regular) checks and sanitation/cleaning of fresh water tanks? I have three plastic water tanks (total 150 gals) on my 49' monohull along with a sea-recovery 1800 fully-automatic water maker. The boat has been kept in virgin islands for the last several years and we are not on-board regularly (more like stay for 10-12 days every two months). We've had no problems with circulating through each tank and have never had any odors or indication of fouled fresh water. We also have a water filter (tap) at kitchen sink and we use it regularly for drinking and cooking. I don't want to start any problems (since there have not been any issues) but thinking I should consider a safe way to put a sanitizer in the water just to be sure. Any suggestions or experiences to share would be most appreciated!
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Old 11-12-2018, 15:42   #2
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Re: Sanitizing Fresh Water Tanks

You can buy Chlorine tablets for water tanks (residential) if below cleaning is not viable. Chances are there is a biological sludge at the bottom of the tanks which is easily removed with a wet/dry shop vac, give a throughout cleaning via inspection port with mild bleach solution and clean (new) scrubber, rinse and refill.
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Old 11-12-2018, 16:25   #3
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Re: Sanitizing Fresh Water Tanks

I always put a cup of bleach in each tank when re-commissioning, fill them up and go sailing for a couple or three hours. Then drain it all out and you are in business. Repeat if it starts tasting or smelling funky but you should probably be OK if you have a watermaker.
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Old 11-12-2018, 16:57   #4
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Re: Sanitizing Fresh Water Tanks

Thank you RBK and sck5. I was thinking on the same lines..
Much appreciated.
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Old 11-12-2018, 17:09   #5
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Re: Sanitizing Fresh Water Tanks

Clean tanks are easy but you have to take care of them. Peggie the head mistress will chime in. She has a book that includes a lot of information on this topic. Don’t forget...... the tanks can get nasty but so do the hoses!!

Good luck
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Old 12-12-2018, 08:54   #6
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Re: Sanitizing Fresh Water Tanks

In the UK at least Lidl do a range of mother and Baby products which includes a very inexpensive sterilisation fluid that will treat a pretty big tank of water. I haven't tried it myself as my boat is in Greece and you can't travel with a 1 litre bottle of liquid but I do use it at home to disinfect my domestic drain pipe from the kitchen sink (long story and a lonnngggg pipe).

Best thing about this stuff is it doesn't leave a nasty taste like Chlorine tablets or Bleach can do and it isn't as toxic as Chlorine or Bleach.

Worthy of consideration anyway
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Old 12-12-2018, 08:54   #7
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Re: Sanitizing Fresh Water Tanks

I don't like the taste of chlorine, I have found that using hydrogen peroxide a high % solution works as well, safe and relatively inexpensive
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Old 12-12-2018, 08:56   #8
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Re: Sanitizing Fresh Water Tanks

I have been using the following formula for years, we just do it once a year. There is a fine line between not using enough bleach to sanitize the tank and using too much bleach which may attack plastic and rubber components of your water system.

A couple of tips I have learned:
Bleed until you smell bleach at each faucet, do hot and cold water separately.
We always just drain the tank once and refill. Have never had an issue with excessive bleach odor.

* CAUTION: DO NOT USE FOR GAS AND/OR FUEL STORAGE *
To assure complete sanitation of your potable water system, it is
recommended that the following procedures be used. This applies if it
is a new system, one that has not been used for a period of time, or one
that may have become contaminated.
(1) Prepare a chlorine solution using one gallon of water and 1/4 cup of
Clorox or Purex household bleach (5% sodium hypochlorite solution).
With tank empty, pour chlorine solution into tank. Use one gallon of
solution for each 15 gallons of tank capacity.
(2) Complete filling of tank with fresh water. Open each faucet and drain
cock until all air has been released and entire system is bled.
(3) Allow to stand for three hours.
(4) Drain and flush with potable water (IMPORTANT)
(5) To remove excess chlorine taste or odor which might remain,
prepare a solution of one quart vinegar to five gallons water and allow
this solution to agitate in tank for several days by vehicle motion.
(6) Drain tank and again flush with potable water (IMPORTANT)
The above recommendations conform to Section 10.8 in the A 119.2
code covering electrical, plumbing and heating of a recreational vehicle.
the solution is approved and recommended by competent health
officials.
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Old 12-12-2018, 09:07   #9
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Re: Sanitizing Fresh Water Tanks

To super chlorinate your tanks you want a dose of 50ppm of 5% sodium hypochlorite bleach. Basically the regular el cheapo stuff from the supermarket is fine so long as it doesn't have special scents and other crap in it.

I do this once or twice a year, leave for a good few hours to a day then flush at least twice.

For regular storage the dosing level is 0.2 ppm
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Old 12-12-2018, 09:19   #10
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Re: Sanitizing Fresh Water Tanks

If your water maker uses tank water for it self cleaning cycle, even a small amount of bleach in your tanks will forever ruin your water maker. The membrane cannot tolerate bleach.

If you choose to use bleach to sanitize your tanks be sure the tank your water maker draws cleansing water from is separate from the other tanks as it must contain no bleach.

I plumb my water maker to use water it is previously made for cleaning. I run it through the water maker several times and then draw the clean water back for the cleaning cycle.
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Old 12-12-2018, 10:01   #11
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Re: Sanitizing Fresh Water Tanks

Quote:
Originally Posted by MIRELOS View Post
I don't like the taste of chlorine, I have found that using hydrogen peroxide a high % solution works as well, safe and relatively inexpensive
Chlorine solution is commonly used in industrial and drinking water treatment facilities where precise application and monitoring is typical. Boaters can't usually nor are they capable. Consequently, while the residual taste is irritating, the prolonged ingestion is worse.

People on the internet advocating for using Cl are doing everyone a disservice. As a health professional, I'd strongly suggest they be ignored.

Rather, higher concentration peroxide is widely available, more effective, has a greater persistency (a good thing), is more forgiving of dosage errors and isn't unsafe for children.

if one maintains clean tanks, Cl solutions is usually unnecessary. If the tank waster is contaminated, Cl solutions don't guarantee anything except fleeting results while often exacerbating the problem
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Old 12-12-2018, 10:46   #12
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Re: Sanitizing Fresh Water Tanks

Thank you all for your recommendations and experience. capstu brings up a very enlightening point about my water maker. the system has an auto fresh water flush that runs (approx 10 mins) after making any amount of water. It draws from the fresh water tank (not sure which one of the three) and flushes the filters etc and then water goes out the brine thru-hull. so any residual bleach in my fresh water tanks may/or may not get into the water maker membrane. Not sure I'd want to take that chance. Will contact Sea Recovery as well for advise. Lastly, I think the use of hydrogen peroxide may be a better/safer option. Wondering the effective dose/dilution?
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Old 12-12-2018, 11:07   #13
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Thumbs up Re: Sanitizing Fresh Water Tanks

Thetford Fresh Water Tank Sanitizer - I didn't believe it, then I used it - $10 on Amazon 1 kit [ 24 ounce cleaner and 24 ounce sanitizer ] does around 100 gallon tank.
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Old 12-12-2018, 11:31   #14
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Re: Sanitizing Fresh Water Tanks

Our Outremer is stored in Greneda and sometimes the water is not used for 6 months or more . The first couple of years I emptied the tank and refilled but not having any issues now I dont bother. I use my oil change vacuum pump to vacuum the bottom of the tanks but as I use a house hold filter inline to fill the tanks and the water maker there is not much there .
I am in the not broke dont fix department on this one . It you add chloine to the tank make sure your charcoal filter for the water maker is up to snuff otherwiseyou can dammage the membrane
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Old 12-12-2018, 14:36   #15
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Re: Sanitizing Fresh Water Tanks

My understanding is that most municipalities use chlorine in their potable water systems.
So if you get water in a Marina in the US it most likely has chlorine in it.
Chlorine will dissipate out of water on its own. You can facilitate the process by leaving a pot or jug out to sit for 24 hours where the water can "breathe ". Good idea for watering house plants ( or people ) which don't tolerate chlorine well.
When I put water into the tanks of my boat I add a cup of Clorox ( chlorine diluted ) into each of my 4, 25 gal water tanks. This way I know the tanks are sterile.
I don't mind using this water for washing dishes or anything else,,,,even showers.
Our drinking water is often bottled water. We can always let our tanked water sit to dissipate the chlorine for drinking water if we need to.
Hydrogen Peroxide needs to be Food Grade to be added to your water system. Your talking over $0.40 per oz to buy it v/s $0.11 per oz.for Clorox.
Bottled water is $0.01 to $0.02 per oz on Amazon.
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