Proper water tank sanitizing bleach amount

[Davidasailor26]

For the last several years I’ve started the season by commissioning the water tanks with the bleach ratio Peggie recommends. Her amount is 1 quart per 50 gallons of water, which she says conforms to “section 10.8 in the A-1 192 code covering electrical, plumbing, and heating of recreational vehicles”. Then today I read a Practical Sailor article from their newsletter ( Decontaminating a Tainted Water Tank - Practical Sailor ) which says to use 1/8 cup per 10 gallons of water. The Practical Sailor article cites ANSI A119.2 section 10.8. On my 95 gallons of tankage that’s a difference between 61 ounces of bleach and 9.5 ounces. I can’t find either of those codes to see what they actually say. Anyone have any idea on what causes this difference and if 9.5 is as good as 61?

 

[Rich Stidger]

I use 1 quart per 250 gallons. I can't remember from where I got that ratio. Don't take it as gospel. It could be wrong; it is just what I use. So far I have not had excessive chlorine taste or smell and I see no evidence that my tanks are nasty. I normally do two full rinses after the bleach treatment. I think I leave the bleach in about 3-4 hours.

 

[RitSim]

A great question. I looked for public water supply data and found this example

http://web.cecs.pdx.edu/~fishw/UO_HOCl%20Solution%20Calculations.pdf

This calc is for 550 gal and the Hypo is 12.5%. I believe standard household bleach is 5%
So using the equation I get .667 # of hypochlorite or 16.5 oz at 12.5% multiply by 2.5 to get 5% solution requirement and get 46 oz. This is also a shock dosage at 200mg/l. max drinking water is 5mg/l with a minimum of 2 mg/l
So Peggy's dosage is about 140 mg/l and the 1/8 cup per 10 gal is about 34mg/l.

I like the stronger solution but the other probably works as well (maybe more time) - in either case you need to get down to 5mg/l. However, the excess and flush probably is going to end up in the river/lake/ocean which is not good.

 

[Davidasailor26]

A great question. I looked for public water supply data and found this example

http://web.cecs.pdx.edu/~fishw/UO_HOCl%20Solution%20Calculations.pdf

This calc is for 550 gal and the Hypo is 12.5%. I believe standard household bleach is 5%
So using the equation I get .667 # of hypochlorite or 16.5 oz at 12.5% multiply by 2.5 to get 5% solution requirement and get 46 oz. This is also a shock dosage at 200mg/l. max drinking water is 5mg/l with a minimum of 2 mg/l
So Peggy's dosage is about 140 mg/l and the 1/8 cup per 10 gal is about 34mg/l.

I like the stronger solution but the other probably works as well (maybe more time) - in either case you need to get down to 5mg/l. However, the excess and flush probably is going to end up in the river/lake/ocean which is not good.

Good find. Thanks. Good to see that both are somewhere between the maintenance and maximum shock amounts.

In terms of getting back below the maximum drinking dosage of 5mg/L - My smaller tank is about 35 gallons, which is 132 liters. So I’d need to have less than 5*132=660 mg of chlorine in the full tank to be below 5 mg/l. My city water report claims the water coming in has 0.6 to 3.78 ppm of chlorine. So if I drain as much bleach solution as possible then pump in 35 gallons of city water, (assuming 3 ppm of chlorine) I’m pumping in 396 mg, so I can’t exceed 264 mg of residual chlorine from the bleach solution. At Peggie’s concentration that means making sure there’s not more than 2 quarts of purge solution left in the tank before I start filling it again. I think my tanks, even when “empty” have more than that much water sloshing around, which explains why I need to pump out that first full tank to get rid of the chlorine smell. If I used Practical Sailor’s concentration the first full tank would be under 5 mg/l as long as I leave less than 2 gallons of bleach solution in the “empty” tank. So maybe with the PS solution I could just start using the first full tank after pumping out the bleach, instead of needing to pump it out.

 

[Don S/V ILLusion]

One word of caution - Be careful when converting from mg chlorine to volume as it changes depending on hypochlorite concentration being used.

 

[SoSound]

Wow! Thanks, for dragging me down this rabbit hole...
I had a brief exchange with Peggy, earlier this year about a spreadsheet that I had found and hoped to use to calculate how much bleach to use; Smelly “fresh” water

WRT the original question, here; "...what causes the difference..." in the recommended 'amounts'? I think it comes down to recommended concentrations for different methods used to treat specific components of a water system. In looking at the spreadsheet that I have (purpose; to calculate the amount of bleach to use in a specific volume storage tank);

• A concentration of 200 mg/L is referred to as "Spraying or brushing on..." (to a surface?), and not included in the spreadsheet. In the document that @RitSim linked, there are photos of storage tanks whose capacities are obviously greater than the 550 or 850 gallons of solution which are the subject of the sample calculations, likely to be surfaces to be sprayed or brushed with 200 mg/L solutions.
• A concentration of 10 mg/L is used to fill a "tank or reservoir", and allowed to stand for 6 or 24 hours.
• A concentration of 50 mg/L is used to fill a "reservoir", and allowed to stand for 6 hours.

Variations are referenced (in the spreadsheet that I have) for both 10 and 50 mg/L concentrations when used for "pipes" or "wells", and allowed to remain for 24 hours in each case.​

Obviously, we don't want to consume such high concentrations, so we flush the tanks after the appropriate treatment period.

My question, what is the best method for treating our small water systems, and what is the best method for flushing residual chlorine? My thoughts are that, once the initial treatment solution has been drained from the domestic water tanks, that I probably don't need to completely refill them to remove the remaining high levels of chlorine. I could probably get most of that out with a quarter of a tank or so of additional flushing. I also decided that I could use some of that flushing water to run through my holding tank this past spring.

I'll be watching. Hope to learn something from this one!

 

[tfox2069]

I wasn't able to find the actual reference, but did find a poster who provided this on an RV site which references a specific paragraph in the ANSI (later incorporated into NFPA):

"I spoke with Don at Vehicle Systems Technical Support, who FAXed me the following information (ANSI/NFPA 1192 paragraph 7.3.7 dated April 2005)regarding maximum concentration of chlorine versus time with the Aqua Hot System:

Maximum Chlorine Concentration = 100ppm for one hour then drain and flush with potable water. (100ppm = 1/2 cup bleach in a 1 gallon solution for every 15 gallons.)

Recommended Chlorine Concentration = 50ppm for four hours then drain and flush with potable water. (50ppm = 1/4 cup bleach in a 1 gallon soluton for every 15 gallons.)"

 

[tfox2069]

BTW, you can go here and read the regulation online for free (you just have to register).

NFPA 1192: Standard on Recreational Vehicles

<p>1.1* Scope. This standard shall cover fire and life safety criteria for recreational vehicles. A.1.1 Those members of the engineering profession and others associated with the design, manufacturing, and inspection of recreational vehicles have been aware of the need for uniform technical...

www.nfpa.org

FWIW I looked up the "paragraph" referenced above, and it doesn't exist in the 2005 edition of the ANSI, and nowhere in the "Plumbing Systems" section (which includes the referenced paragraph number) is there a recommended chlorine concentration. I'd rely on Peggy and/or Practical Sailor. Both are authoritative as far as I'm concerned.

 

[DArcy]

I had a strong Sulphur smell in my water this year. I tried Peggy's dosage of chlorine, left for 24 hours, and it made no difference to the smell. I found a reference to use 1 cup of 3% hydrogen peroxide per 10 gallons of water. I used 1 liter in my 50 gallon tank which was not quite full and it got rid of the smell completely.

 

[srimes]

Chlorine test strips are cheap if you want to make sure it's low enough and you're trying to use the minimum amount of flush water.

 

[Meriachee]

Should be enough bleach to wipe it out in, like, one minute

sorry folks, i couldn't resist.

 

[svluigi]

Hello, I followed Peggy’s instructions. But now I am flushing out the chlorine water and the foam I believe is causing the pump to be sluggish. How long until the bleach foam disappears?

 

[Davidasailor26]

I’ve not had any problems with foam using the bleach. Did you use conventional chlorine bleach or some kind of detergent mixture? Also, check if you have any in-line filters or an aerator on your faucet. The bleach can cause debris to flake off and clog those filters.

 

[Peggie Hall HeadMistress]

Sounds like you may not have used bleach labeled "non-foaming." I have no idea what's used in bleach to cause it to foam, but doubt it's detergent. Try letting it sit overnight to see if it "settles down." If it doesn't, I'll do a little research to find a solution.

--Peggie

 

[Johnb]

I don't know how authoritative the below is but it does make interesting reading.

Home - Mama Say What?!

Mama Say What?! is your ultimate lifestyle hub, dedicated to enriching every facet of your journey. From nurturing family bonds to fostering a happy home,

homeardent.com

 

[Peggie Hall HeadMistress]

That might apply to a waste holding tank, but this is a water tank.

--Peggie