Water Tanks over Winter

[LordByron]

I am about to leave my boat for 2 to 3 months over winter here in the south of France. There is no chance of frost.

Do I leave the tanks full, empty or somewhere in between? Any suggestions?

And what additives do you recommend?

[Lepke]

I use a pool test to add a small amount of chlorine (bleach). I shoot for the lowest amount that shows on the test. Full or empty, air moves in and out of the breather with heat and cold, and will eventually carry bacteria into the tank.
I live aboard and make my water. My tanks are always in use. I still have to bleach every few months. It's better to never allow a large bacteria colony. Even dead they leave residue.
One option is to completely drain your tanks, leaving no water.

[StPeteRob]

I've always been told to use vinegar instead of chlorine because of the various gaskets and seals on the tanks, plus it has the added bonus of removing mineral buildup.

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[thinwater]

The obvious answer is that they should be cleaned once each year, and that this is a perfect opportunity to get them bone dry (vacuum). Put it up clean, just as you would the dishes at that summer home. Would leave a jug of water in your home for 2 months and then drink from it? I doubt that.

But a minimum chlorine residual is a lazy answer.

[westwinds]

If drinking water is from a surface source (river, lake) there will be traces of organics, like tannins for instance from leaves, which microbes can metabolize. Some wells also have organics in the water. Now microbes that do not make odors need oxygen for metabolism. Anaerobic bacteria grow where there is no oxygen, but produce odors, think septic tank kinds of odors. Now if aerobic bacteria use all the oxygen in the water to metabolize organics, then the anaerobic ones take over and you would not want to drink it for the smell. The amount of oxygen in a liter is 6 to 12 milligrams per liter, in round numbers, say 1 part in 100,000. That's not much oxygen to keep the water aerobic. What I think should be done is put an aquarium bubbler in the water tank to keep it aerobic. Hook it to a solar panel with enough power to run the bubbler when the sun is up, say about six hours a day if there is no shore power. It would probably run on a one amp 18 volt solar panel, which would probably drop to 12 volts with a little more amps output. Check your bubbler and panel for amps and volts for a good match. Probably the bubbler would not need to go all the way to the bottom of the tank, so less pressure and power needed. I have not done this myself, but I think it would work. Someone should try this. I am sure forum readers would like to know if this works. It would save a awful lot of clean out time in the spring.

[Steve Bean]

As mentioned by westwinds, water from surface sources and some well waters can contain organic compounds. Treating such water with chlorine produces a group of compounds called trihalomethanes (THMs) which include chloroform, bromoform, and a few other things with even longer names, not good for us. Carcinogenic, that is. The water supplier should be able to provide analysis of the water. Storing the tank empty and dry eliminates the problem, and you can start your next season with fresh water.

[westwinds]

Can anyone tell me how long drinking water held in a tank will last before it is no longer pleasant to drink? I know this is going to vary depending on the organics in the water and the temperature. If you have any experience with how long the water takes to go bad, maybe you can tell us what kinds of temperatures you experienced and whether the water source for your tank is from a surface water or a well?

By the way Steve has brought up a point about total trihalomethanes that is not discussed much by the public health types to the general public. Their belief is that we will get some excess cancers, but the benefit of being able to kill pathogenic bacteria cheaply out weights the cancer problem. I would be willing to pay more for disinfection by ozone or ultra violet. Unlike chlorine, both these disinfectants will kill giardia cysts. A public water treatment removes these cysts by filtration, not disinfection with chlorine. Google giardia, it is prevalent in fresh water lakes from wild life and you will note that it is not a disease you want to experience. I will use ultra violet disinfection for any water I take on board if there is any question about its source.

[thinwater]

Originally Posted by westwinds

Can anyone tell me how long drinking water held in a tank will last before it is no longer pleasant to drink? I know this is going to vary depending on the organics in the water and the temperature. If you have any experience with how long the water takes to go bad, maybe you can tell us what kinds of temperatures you experienced and whether the water source for your tank is from a surface water or a well?

By the way Steve has brought up a point about total trihalomethanes that is not discussed much by the public health types to the general public. Their belief is that we will get some excess cancers, but the benefit of being able to kill pathogenic bacteria cheaply out weights the cancer problem. I would be willing to pay more for disinfection by ozone or ultra violet. Unlike chlorine, both these disinfectants will kill giardia cysts. A public water treatment removes these cysts by filtration, not disinfection with chlorine. Google giardia, it is prevalent in fresh water lakes from wild life and you will note that it is not a disease you want to experience. I will use ultra violet disinfection for any water I take on board if there is any question about its source.

The first question is like "how long is a piece of string." The obvious answer is that if the water is properly purified, practically forever.

You are far, far more likely to die of infectious disease than cancer from trihalowmethanes. I consider that to be read herring, or at least a lighten strike sort of fear. Keep your eye on the ball.

1. Neither ozone nor UV leave any resisdual in the tank. Thus, if any organisms survive, and they will, they will multiply out of control. This is not acceptable for a distribution system and it is not acceptable in your tank.
2. UV takes a lot of power for tap use because it must be left on (bulbs have long warm-up time). As for UV treatment before loading, the required treatment unit to kill both bacteria and cysts in unfiltered water (you will have to filter) at 10 gpm is impractical. Folks won't like waiting behind you.
3. trihallow methanes can be minimized by not over-chlorinating. Measure the dose.

There are proven protecoles that are safer and more reliable than the road you are considering. Quite easy, actually.
1. Prefilter to remove solids. Clean the tank annually. Nothing works if the tank is not clean.
2. Chlorinate. Measure the dose, it is actually very, very low.
3. Secure the vent. Bugs can crawl in.
4. Filter NSF 53 at the tap for cysts. If this is done with a carbon block filter it will remove the chlorine and much of the THMs.