[pdqaltair]

How much bleach is needed to sanitize and to provide ongoing disinfection has been flogged to death here and by EPA/WHO/ANSI. But there is always concern that bleach will slowly eat away at aluminum tanks. No question, it does, I've run the coupon tests. If there is a solid residual in the tap water, it is enough to shorten the life of a tank in regular use. Hydrogen peroxide is suggested as an alternative; it is often strored in aluminum tanks. Additionally, it will neutralize bleach/free chlorine in water, converting it to less agressive Cl-. It would be interesting to do some corrosion tests on this effect... but niether EPA or WHO consider it a valid disinfectant and I can find nothing authoritative on the web. Perhaps my Google Fu is weak.

My understanding has always been that for sanitizing it must be used nearly straight up (3%). I've read that up to 1000 ppm is authorized for drinking water (EU chemical company), but that would be rediculous in use, requiring a case per fill-up. A single bottle would only reach ~ 30 ppm, and I'm pretty sure that is not enough unless combined with other treatments.

Any authoritative refferences? "I've been doing X for years" does not count--though I'm sure you have, others have been doing nothing and remained healthy. There must be some agency that has published something.

 

[newhaul]

I'm curious about that as well

 

[newhaul]

Here's what I have found so far. Using Hydrogen Peroxide (H2O2) to purify water | Survival Recovery " The EPA has not approved this method of water purification.
Quote:
Hydrogen peroxide (H2O2) is rarely used in drinking water treatment as a stand-alone treatment process. H2O2*is a weak mirobiocide compared to chlorine, ozone, and other commonly used disinfectants. Consequently, it is not approved by regulatory agencies as a stand-alone disinfection treatment process.
However, there are a number of technologies where H2O2*is used as part of the treatment program. (more&#8230
Trusted sources recommend adding 1/8 c of Hydrogen Peroxide*to 1 gallon of h20. This process eliminates many of the*contaminants*that can be found in untreated water. It is suggested that you let the purified water sit for at least 24 hours. Allowing treated, *purified water to sit overnight is a common practice.
Using Hydrogen Peroxide to*purify water has been shown to create a higher level of oxygen in water which in turn is healthier for the body. Hydrogen Peroxide has been known to be a cleansing agent for eleminating toxins in the body's system. Added in small amounts to water, Hydrogen Peroxide's benefits can be a healthy alternative to bleaching water for*safe clean water." Hope it helps answer the question

 

[IStream]

If you don't have E. coli or other pathogens growing in your tanks, is there really any need to disinfect at all? I understand the yuk factor of considering what the inside of my tanks look like after 20+ years but it seems that filtering is a pretty effective strategy to prevent illness and improve taste.

 

[pdqaltair]

^^ Yes, I have seen that and similar postings. Bear in mind that is 3-4 pint bottles per fill-up, which is quite a bit. I doubt anyone does that.

 

[Stumble]

I wonder if a UV light wouldn't be a better option than chemical treatments. At least for a metal tank (the UV would probably destroy plastic ones). It's highly effective at sterilizing water, and won't leave any residue.

 

[RichH]

In high purity water systems H202 is rarely used due to the expense of H202

Those who 'do' use hydrogen perooxide: use 30,000 ppm (WPA) soak at 120 minutes. Others use 10% - of concentrated H202 which is 35% concentration - (v/v) for 2-3 hours ... and thats starting out with a 35% solution of 'food grade' H2O2. 'Drugstore' H202 is approx 3-5% concentration; and is of such insignificant 'potency' that its considered 'useless' for sanitization purposes.
H2O2 is much less 'effective' for sanitization than simple Chlorination.

The real answer here is to use 10-15 ppmw free chlorine (Clorox @ 40 oz. per 100 gallons) and soak the tank for 30-60 minutes .... and simply 'enjoy' the products of aluminum chloride, and a new tank in about 15 years. Of course thats if the tank does not exhibit a 'calcyx' - a slimy, massive bacteria colony growing on the walls of the tank.

The 'hands on' winner for sanitization is Peracetic acid; BUT, you need the 'dipsticks' to assay for indications of improper flush/rinse when done, as Peracetic kills 'everything' .... including human tissue.

 

[RichH]

I wonder if a UV light wouldn't be a better option than chemical treatments. At least for a metal tank (the UV would probably destroy plastic ones). It's highly effective at sterilizing water, and won't leave any residue.

Not really, as the water tank on a boat is a 'stagnant system'. UV treatment needs a 'constantly flowing and constantly recirculating' water system to be effective. All the dead-legs on a a boat's water system are simply 'incubation sites' for bacteria, etc. Such would be a complex and expensive 're-design' on a boat to lessen all the non-flowing 'dead legs'. UV is a 'power hungry' system.

 

[capta]

I've been looking into the UV lights as a purifier addition to our watermaker. From what I've read, unless you are sailing in particularly dangerous waters (like up rivers near cities) it isn't yet a practical, affordable system, though they apparently do work on biological contaminants. When last I checked the bulbs needed changing on an annual basis, so it's not an install and forget item. Hopefully soon these will follow the solar panel drift toward lower prices.

 

[pdqaltair]

RichH:

What is the source of the table? The values square with what I understood, but it always like to understand the source.

What about drinking water disinfection? I've read refferences to 30-100 ppm, but without basis. this strikes me as 3-10 x too low, given the levels requierd to sanitize, and the required amount to disinfect would thus be unhealthy.

Which explains EPA/WHO stance on the subject; H2O2 is not an effective agent.

But is there a validated drinking water number or range?

 

[GeorgeB]

O.k., a couple of dumb questions. What is the difference between pool chlorine and Clorox? (I assume I don’t use the one with fabric softener, but what about the “additional whiteners kind”?) My tanks are approx. 30 gallons so I would be using 12 oz. (2 Pints) of bleach in each tank? Is the water still drinkable? Or do I drain and refill? I mainly use only one tank in order to not let things stagnate too much. Can I mix a 50:50 solution of cheap vodka and water and let it slosh around the bottom of the tank that I’m not normally using? After I sanitize the aft tank should I go back to switching back and forth? (The water would “sit” normally for 3-4 months before the tank would get switched.)

 

[pdqaltair]

a. Plain bleach. Some of the "other whiteners" are not things you should drink. Plain sodium hypochlorite.

b. This is a good thread on the topic with some long posts with instructions.
http://www.sailnet.com/forums/gener...ing-sanitizing-fresh-water-holding-tanks.html

c. Vodka is not a sanitizing agent if it is diluted. Think about it; you can ferment up to >20% alchohol, so why would we think weak vodka would kill everything? CDC does not recognize rubbing alchol as a sanitizing agent below 40%. So the weak vodka thing is pure urban legand. You would have to fill the tanks with neat vodka, which would be pretty silly.

d. Why not use both tanks regularly, keeping them fresh? Waste some water and keep it running through.

Keeping water fresh is either simple, once you think through the whole process, or very complicated. Perhaps this blog post will help, though it is the short version. The full version will be published this winter.

Sail Delmarva: Drinking Water Filtration--The Short Version

 

[RichH]

RichH:

What is the source of the table? The values square with what I understood, but it always like to understand the source.

What about drinking water disinfection? I've read refferences to 30-100 ppm, but without basis. this strikes me as 3-10 x too low, given the levels requierd to sanitize, and the required amount to disinfect would thus be unhealthy.

Which explains EPA/WHO stance on the subject; H2O2 is not an effective agent.

But is there a validated drinking water number or range?

Actually H202 is a POTENT sanitizing agent. The problem is that the H202 concentrations needed are very dangerous for those who dont have the chemical expertise. Such used to be used routinely in 18 meg-Ω microelectronics / ultrapure chemicals / pharma production. The current trend has been towards PerAcetic Acid for the past 10-15 years.

This chart came from a compendium of the then (~2005) current sanitizations for automated water systems from a 'pure water' conference . If I remember correctly the combined sources was either "Semiconductor Mag." or one of the Bio-Pharma magazines.

For municipal water, I believe, the AWWA still uses 1-2 ppmw Cl (residual) for maintenance dosage (at the spiggot) and 10-15 ppmw for shock sanitization .... but this is for new or CLEAN distribution; not one that is contaminated (bacterial slime/calcyx evident). The old NSF recommendations were essentially the same; but, never acknowledged nor included dosages nor serial soak times for calcyx contaminated systems. A Calcyx is a visible massive bacterial colony - the slime that one feels on the walls of a grossly contaminated system.

 

[RichH]

O.k., a couple of dumb questions. What is the difference between pool chlorine and Clorox? (I assume I don't use the one with fabric softener, but what about the "additional whiteners kind"?) My tanks are approx. 30 gallons so I would be using 12 oz. (2 Pints) of bleach in each tank? Is the water still drinkable? Or do I drain and refill? I mainly use only one tank in order to not let things stagnate too much. Can I mix a 50:50 solution of cheap vodka and water and let it slosh around the bottom of the tank that I'm not normally using? After I sanitize the aft tank should I go back to switching back and forth? (The water would "sit" normally for 3-4 months before the tank would get switched.)

12 oz. Clorox per 30 gallons would be correct for the shock sanitization of 'clean' tankage.
Then ..... you MUST drain/rinse thoroughly before commissioning.

Vodka / EtOH ... Rinse it and then flush it. Its a nutrient source for some species of bacteria. Such is what makes beer and booze 'cloudy'.

Sit for 3-4 months ???? ... empty / drain the tank when you lay-up for long periods.
A 'dry' tank will grow damn few microorganisms. A filled unused tank is a stagnant breeding incubator for microoganisms.
Hint: Thoroughly clean the slime (bacterial calcyx) off the walls of the tank on your home toilet; open the tank 3-4 months later and feel the regrowth of the bacterial calcyx on the tank walls. Your boat tank doesnt get that amount of 'active flush' so guess what's happening inside your boat tank especially if you dont keep the chlorine level to about 1 part per million ????? http://www.sailnet.com/forums/images/smilies/frown.gif
1 part per million chlorine concentration in water will be approx. the 'barest odor' of chlorine that you can detect with your (wife's) NOSE.