When to Purify Water Tank?

[Jonny A]

The water in my plastic tank has gone brackish, so obviously I need to purify and flush it. But, am I better off leaving until spring and doing it then, or purifying now and then maybe draining the tank and leave it over the winter? The boat will be out of the water in a few weeks but I don't have a heater onboard for the winter.

 

[Aurai]

Hi, my suggestion is both, drop a tablet (according to dose) in now, drain it for winter. Refill, spring, we refill, dose, empty, refill, halve the dose. Cheers

 

[sarabande]

Empty the tank, flush it and the pipework through with the algicide of your choice (bleach, milton, etc) then refill with clean water with a preventive dose of bug killer. If you leave the tank empty you run the chance of introducing aerobic bacteria . However, depending on the configuration of your tank and pipework, it may freeze if full, so on balance, empty, sterilise, refill, flush, empty, and block the breather pope and filler, with a big label to remind you about the breather.

 

[thinwater]

My advice is based on experience, testing, and a colder climate.

BTW, brackish indicates it contains considerable salt but less than the ocean. From OED:
brackish
adjective

1. (of water) containing salt and tasting of it in an unpleasant way

a. Yes, add a bleach containing additive (about 1/8 cup per 10 gallons for sanitizing, according to ANSI) and circulated through the system. Might as well get a small jump on it now. Flush with water after a few hours.
b. Pump the system empty and vacuum bone dry. You wouldn't put glasses away wet, wound you?
c. Antifreeze the water system either with glycol (minimum 27% unless you want to grow bugs) or blow it out. Glycol is safer in really cold climates because it is difficult to be SURE you have it dry. NEVER put glycol in the calorifier or tank. You won't add enough, the bugs will ferment, and it will take forever to sanitize the system in the spring.
d. Sanitize again in the spring, as above. In the future, once per year should be enough... IF you dry the tank AND use enough glycol to prevent fermentation.

People tend to skimp on glycol or alcohol, thinking "it does not get that cold here." It is NOT just about temperature, it is about pickling the pipes. It MUST be at least 27% to prevent growth. This is well known in industry. Insufficient winterizing is probably the leading cause of funky tanks.

 

[peter gibbs]

The water in my plastic tank has gone brackish, so obviously I need to purify and flush it. But, am I better off leaving until spring and doing it then, or purifying now and then maybe draining the tank and leave it over the winter? The boat will be out of the water in a few weeks but I don't have a heater onboard for the winter.

Give it a good dose of Milton or equivalent now. Leave standing 24 hrs, No need to fill the tank, wash around with clean sponge to clean all surface, don't forget to dose / scrub the feeder pipe. Remove all.

Refill to 10% or so and dose again, leaving for winter - this much water might freeze but will not damage the tank. Remove in spring and fill etc.

PWG

 

[thinwater]

...Refill to 10% or so and dose again, leaving for winter - this much water might freeze but will not damage the tank. Remove in spring and fill etc.

PWG

Probably not in most of the UK, but I have seen tanks split wide open in colder climates with just 10%. I just depends on the geometry, temperature, and sequence of events. Folks don't risk that here.

 

[VicS]

My advice is based on experience, testing, and a colder climate.
a. Yes, add a bleach containing additive (about 1/8 cup per 10 gallons for sanitizing, according to ANSI) and circulated through the system. Might as well get a small jump on it now. Flush with water after a few hours.
b. Pump the system empty and vacuum bone dry. You wouldn't put glasses away wet, wound you?
c. Antifreeze the water system either with glycol (minimum 27% unless you want to grow bugs) or blow it out. Glycol is safer in really cold climates because it is difficult to be SURE you have it dry. NEVER put glycol in the calorifier or tank. You won't add enough, the bugs will ferment, and it will take forever to sanitize the system in the spring.
d. Sanitize again in the spring, as above. In the future, once per year should be enough... IF you dry the tank AND use enough glycol to prevent fermentation.

People tend to skimp on glycol or alcohol, thinking "it does not get that cold here." It is NOT just about temperature, it is about pickling the pipes. It MUST be at least 27% to prevent growth. This is well known in industry. Insufficient winterizing is probably the leading cause of funky tanks.

When you suggest glycol antifreeze are you suggesting an ethylene glycol ( ethanediol) based engine antifreeze or using straight ethanediol ?

Would the propanediol based antifreeze, sold as "non toxic" antifreeze for winterizing RV water systems, be just as effective

 

[fredrussell]

Brackish water in tank is a new one to me. How is sea water getting in there, through the filler cap/overflow?

 

[Jonny A]

Thanks for the advice everyone. Just to clarify: I said 'brackish' but don't actually mean it tastes of salt, just tastes 'off'.

 

[Boathook]

I feel that a lot of water issues is due to lack of turnover. I also get the impression that there are more issues with the flexible plastic pouch tanks rather than stainless steel or solid plastic.
If I feel that I'm not turning water over enough I empty the tanks before refilling. This assumes that the water I'm filling up with is OK and that it is via a hose, preferably mine.

 

[thinwater]

When you suggest glycol antifreeze are you suggesting an ethylene glycol ( ethanediol) based engine antifreeze or using straight ethanediol ?

Would the propanediol based antifreeze, sold as "non toxic" antifreeze for winterizing RV water systems, be just as effective

Only propylene glycol (propanediol), often sold as non-toxic RV antifreeze, should be used in a potable water systems. It is essentially non-toxic, as opposed to ethylene glycol, which is acutely toxic to mammals. Ethanol-based AF can also be used, but it is harder on elastomers. Ethylene glycol can be used in engine and blackwater (sewage hold) systems so long as proper care is given to not leaving it open so that pets can drink it. Both glycols are recyclable by the same vendors. All three are low-toxicity in the marine environment (Google SDS sheets) and very biodegradable.

Interestingly, it takes about the same minimum concentration to pickle the system, whether EG, PG, or ethanol. All three can ferment if too weak.

[decades in the glycol manufacture and formulation industry]

 

[VicS]

Only propylene glycol (propanediol), often sold as non-toxic RV antifreeze, should be used in a potable water systems. It is essentially non-toxic, as opposed to ethylene glycol, which is acutely toxic to mammals. Ethanol-based AF can also be used, but it is harder on elastomers. Ethylene glycol can be used in engine and blackwater (sewage hold) systems so long as proper care is given to not leaving it open so that pets can drink it. Both glycols are recyclable by the same vendors. All three are low-toxicity in the marine environment (Google SDS sheets) and very biodegradable.

Interestingly, it takes about the same minimum concentration to pickle the system, whether EG, PG, or ethanol. All three can ferment if too weak.

[decades in the glycol manufacture and formulation industry]

Thanks for clarifying.

 

[Momac]

I would be draining that off and flushing through at least another tank full of fresh water via opening the taps so the pipework is flushed .
If that doesn't resolve the matter then consider some sterilising solution treatment.
I used to use sterilising treatment annually but recently just flush through with fresh water in the spring.
Over the summer we are adding water most weeks so not really concerned about

 

[peter gibbs]

Thanks for the advice everyone. Just to clarify: I said 'brackish' but don't actually mean it tastes of salt, just tastes 'off'.

I note comments on adding chemicals other than Milton type cleaners. This would be totally unnecessary for the condition you describe and would require extensive purging come the fitting out. I would never do such a thing.

PWG