Freshwater tank contamination

[Warrior35]

My boat, Bow Bells, was out of the water for 6 weeks earlier on in the summer which meant that the fresh water was not kept as cool as it would have been afloat. We (my wife) noticed after re-launch that it smelt...the tank was flushed through with fresh and purification tablets were added. After 2 weeks cruising, the smell is slightly better but the colour is pale green. Amazing we got back at all really. Grateful for most effective solution.

 

[Talbot]

Puriclean for 24 hours at the recommended dosage with a full water tank, and with the treated water pumped through to taps. use the boat so that it sloshes around. Drain, flush, drain, flush, refill, and replace any water filter - should be good, but I then add a single aquatab at each fill up

 

[Chris_Robb]

Re: Freshwater tank contamination (from Head Mistress)

This is advise I used from the Head Mistress - a regular contributor. I used standard houshold bleach. I would normally only do this at the end of the season - but sounds like you have a cause for doing something now!
HeadMistress
(new user )
16/09/2003 19:33 Re: tainted water


Although most people think only in terms of the tank, the plumbing is actually the source of most foul water, because the molds, mildew, fungi and bacteria which cause it thrive in damp dark places, not under water. Many people—and even some boat manufacturers—believe that keeping the tanks empty reduce the problem, but an empty water tank only provides another damp dark home for those “critters.”

There are all kinds of products sold that claim to keep onboard water fresh, but all that’s really necessary is an annual or in especially warm climates, semi-annual recommissioning of the entire system—tank and plumbing. The following recommendations conform to section 10.8 in the A-1 192 code covering electrical, plumbing, and heating of recreational vehicles. The solution is approved and recommended by competent health officials. It may be used in a new system a used one that has not been used for a period of time, or one that may have been contaminated.

Before beginning, turn off hot water heater at the breaker; do not turn it on again until the entire recommissioning is complete.

Icemakers should be left running to allow cleaning out of the water feed line; however the first two buckets of ice—the bucket generated during recommissioning and the first bucketful afterward--should be discarded.

1. Prepare a chlorine solution using one gallon of water and 1/2 cup (4 oz or 125 ml) Clorox or Purex household bleach (5-7% sodium Hypochlorine solution ). With tank empty, pour chlorine solution into tank. Use one gallon of solution for each 5 gallons of tank capacity.

2. Complete filling of tank with fresh water. Open each faucet and drain cock until air has been released and the entire system is filled. Do not turn off the pump; it must remain on to keep the system pressurized and the solution in the lines

3. Allow to stand for at least three hours, but no longer than 24 hours.

4 Drain through every faucet on the boat (and if you haven't done this in a while, it's a good idea to remove any diffusion screens from the faucets, because what's likely to come out will clog them). Fill the tank again with fresh water only, drain again through every faucet on the boat.

5. To remove excess chlorine taste or odor which might remain, prepare a solution of one quart white vinegar to five gallons water and allow this solution to agitate in tank for several days by vehicle motion.

6. Drain tank again through every faucet, and flush the lines again by fill the tank 1/4-1/2 full and again flushing with potable water.

People have expressed concern about using this method to recommission aluminum tanks. While bleach (chlorine) IS corrosive, it’s effects are are cumulative. So the effect of an annual or semi-annual "shock treatment" is negligible compared to the cumulative effect of holding chlorinated city water in the tank for years. Nevertheless, it's a good idea to mix the total amount of bleach in a few gallons of water before putting it into either a stainless or aluminum tank.

People have also expressed concern about the potential damage to rubber and neoprene water pump parts. Again—the cumulative effect of carrying chlorinated water is far more damaging over time than the occasional “shock treatment.” And it’s that cumulative effect that makes it a VERY bad idea to add a little bleach to each fill. Not only does it damage the system, but unless you add enough to make your water taste and smell like a laundry, it’s not enough to do any good. Even if it were, any “purifying” properties in chlorine evaporate within 24 hours, leaving behind only the corrosive properties.

An annual or semi-annual recommissioning according to the above directions is all that should be necessary to keep your water tasting and smelling as good as anything that comes out of any faucet on land. If you need to improve on that, install a water filter. Just remember that a filter is not a substitute for cleaning out the system, and that filters require regular inspection and cleaning or replacement.
________________________________________
Peggie Hall
Specializing in marine sanitation since 1987

 

[Ships_Cat]

Re: Freshwater tank contamination (from Head Mistress)

We do the same. Some say one shouldn't use household bleach as not pure and produces other products when reacts with organic matter, but think that is scaremongering because the tanks have to be well flushed out after.

Not quite sure what Peggie's concentrations work out at but here in NZ household bleach is normally 3.5% (not 5-7% as in USA) - we use 135ml of 3.5% bleach (added directly to the tank) per 100 litres of water as the shock treatment. The tank will need to be flushed after.

John

 

[HeadMistress]

Re: Freshwater tank contamination (from Head Mistress)

Cat, if household bleach in NZ is only 3.5%, I'd just double the quantities. It is important that whatever the type of chlorine used, that it be a solution of 5-7%. More is overkill...less isn't enough to kill all the "critters."

And while I don't know what's added to bleach in the UK, I think your point that it shouldn't matter too much because it will all be thoroughly flushed out before filling the tank to use the water is well taken.

Btw...what all IS added to household bleach in the UK???

 

[Ships_Cat]

Re: Freshwater tank contamination (from Head Mistress)

Hi Peggie

Bored myself by working it out /forums/images/graemlins/crazy.gif.

135ml of 3.5% per 100 litres water works out to be around 1 US fl.oz of 5% per 8 US gals water.

I think that might be about 1/8 what you recommend (8 US fl.oz/10 US gals I think?) but is a pretty solid hit - think I originally worked it from shore side use in treating tanks. Serves in our case with tanks always clean even though only hit about every 4-5 years, however, our tanks and all pipework are lightproof, they are in continual use year around and we (almost) always use treated town water or rain water (when at sea) for filling so is no significant sediment build up.

If I remember correctly half (ie around 65ml) the 135 ml of 3.5% per 100ml produces a barely drinkable water in the case of bringing questionable water on board (can't remember but think that was also in excess of the 10ppm Cl required to kill resistant pathogens such as Cryptosporidium in 6 hours exposure - someone may wish to work that out).

Important message, in my view, is that people should not be frightened to use household bleach and generally, the more the merrier (unless one is a tank denizen critter) for cleaning tanks. Is certainly many times cheaper than the tablets, etc and probably far more effective (if only because it costs very little to add a great big dollup of it). If used in questionable water and drunk, any risk from the bleach is probably much less than the risk from pathogens if not treated.

As to additives to household bleach, I don't know what is added in UK but here can optionally buy with lemon smell (citronella?) which would be fine, and I suspect it may have surfactants added but never investigated that.

Regards

John

 

[Warrior35]

Re: Freshwater tank contamination (from Head Mistress)

Many thanks guys. Amused by the icemaker advice, seems somewhat irrelevant at my lattitude but when I am cruising in the tropics....