SANITATION OF POTABLE WATER SYSTEM

Rocky Lou

Well-known member
Joined
Aug 2, 2019
Messages
413
Fluid Motion Model
C-302 C
Vessel Name
Sea Suite
Unfortunately, I used the 'fire, ready, aim' method and poured vodka into my water tank, drained and refilled. A bit later, I researched further and read analysis by chemists stating that vodka can enable bacteria growth and either bleach or hydrogen peroxide are recommended. They also noted that commercial products, like those sold at West Marine, often contain toxic ingredients, and bleach alone is better. I don't think there's a lot of vodka for me to worry about and now I'm planning to use the method in the Cutwater manual:
SANITATION OF POTABLE WATER SYSTEM:
SUGGESTED METHOD OF DISINFECTION
Perform the following steps in the order indicated at least once a year:
a. Flush entire system thoroughly by allowing potable water to flow through it.
b. Drain system completely.
c. Fill entire system with a chlorine solution having a strength of at least 100 parts
per million, and allow to stand for one (1) hour. Shorter periods will require
greater concentrations of chlorine solution. See Table Below
d. Drain chlorine solution from entire system.
e. Flush entire system thoroughly with potable water.
f. Fill system with potable water.
Table I shows how much disinfecting agent is required to make up various quantities
of 100 parts per million chlorine solution.
 
And be sure to run all faucets and showers, and if you have them, the fresh water flush toilets, with the highly chlorinated water so that it gets to every part of the system.
 
Also clean the screen/strainer on the water pump. Ours was black when we first cleaned it after trying the the Vodka treatment, yuck! Now we clean the screen and do a bleach disinfect before launch each spring. Fantastic water since. We drink it.
 
I drained the tank and cleaned the strainer, it was not too bad. I'm still confused about how much bleach to use as the recommended amounts are all over the map.

If you look at the Clorox site, it says:
To clean out a water tank, first thoroughly flush the tank using a bleach solution of 1 part Clorox® Regular Bleach per 150 parts water (a 500ppm bleach solution). For 40 gallons, that's about 8 cups of bleach.

If you read the directions posted in the Cutwater 302/32 Manual, it's says ' 100 parts per million chlorine solution', that is 5x as much or 40 cups of bleach...wow!

Then there are a ton of folks on Tugnuts talking about adding much smaller amounts of bleach. Which is right? Did I do the math correctly?
 
By my calculation, 100ppm for 40ga would be 1/16 cup:

40ga*16cups/ga = 640 cups in tank
640 cups / 1000000 = 0.00064 cups (1ppm)
0.00064 cups * 100 = 0.064 cups (100ppm)

So 500ppm = about 1/3 cup bleach per 40 gallons, which seems about right to my intuition for a strong sanitizing solution. That is assuming that "ppm" is of the bleach solution itself.

or did I mess up the math as usual 🙂 ?
 
On a bottle of Clorox, it lists the ingredients of 4.5% Sodium Hypochlorite, the active ingredient, the rest is other ingredients (water). Then it says 4.275% available chlorine. Sooo when it's referred to as ppm, do we use what's in the bottle as one ppm, or do we have to take the active ingredients as ppm? Is the devil in the details? Where are our chemists :?:
 
I use a 1/4 cup Clorox bleach for my 30 gallon water tank. I do this twice a season or every 2 months if we are winter cruising. It is amazing how a 1/4 cup of bleach will leave a odor of bleach in the sinks. I mix up a gallon 1/4 cup + water pour it in the tank. Next fill the tank. I then open each faucet, head, galley, cockpit shower, and flush head. I run the water until I smell the bleach. I let it sit in the tank and water lines for a few hours. Drain the tank using the faucets. I refill the tank and drain again. Fill the tank and change the water filter in the ( Dupont whole house water filter ). We drink the water from the tank. 5 years of drinking the water we have not had an issue and the water taste ok. We haven't gotten sick !!! I know that is not a good gauge of it being sanitized but I'm going with it 😀
 
As I mentioned, I'm referencing what was covered by FM in 'As the Prop Turns, Maintenance #1": "To make 10g of Bleach Solution, you would start with 9 gallons + 15 cups of water, and then add 1 cup + 1 Tablespoon bleach", hence, 40g would be 4 cups + 4 Tablespoons bleach; 80g would be 8 cups + 8 Tablespoons bleach...simple math so far I think. Here's the Clorox link: https://www.clorox.com/how-to/disin...sinfecting-with-bleach/bleaching-water-tanks/

I found this calculator for Chlorine dilution:
https://www.publichealthontario.ca/en/health-topics/environmental-occupational-health/water-quality/chlorine-dilution-calculator

7.4% sodium hypochlorite is in Clorox® Disinfecting Bleach, more concentrated than most other bleach products.

Hence, a 500ppm solution would require:
0.57 gallons (US) of bleach to 79.43 US gallons of water (close to 8 cups + 8 tablespoons above)
0.28 gallons (US) of bleach to 39.72 US gallons of water
0.21 gallons (US) of bleach to 29.79 US gallons of water

Kindly advise if I'm losing it 🙂 I think we will all agree it's not well explained and using both water ratio and PPM adds to the confusion.
 
Very interesting. That is a LOT of Chlorox. I suppose a few gallons stay around even when "empty", in the pipes, water heater, bottom of tank, etc. At that concentration, seems like it might take a second to bring down the smell?
 
Bob: I think there is a typo in your message. The Practical Sailor article says 1/8 cup of bleach to 10 gallons of water, not 1/8 cup per gallon. Comments to the article indicate 1/8 cup to 8 gallons. Either way a half cup of bleach for a 30 to 40 gallon tank seems more appropriate when left to sit for 4 hours before flushing.
 
It's good to see the soak time brought into the process. The Clorox method is a quite a lot of bleach. I found other discussions on the same question:
https://forums.sailboatowners.com/threads/proper-water-tank-sanitizing-bleach-amount.1249926619/

Oct 1, 2020
#1
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?
 
Thanks S. Todd for the typo catch... corrected now..... as I head over to the boat to start the process... 🙂
 
Note that the last line of the formula in the Practical Sailor description is to "Double the concentration for a 1 hour soak". That is consistent with all of the past advice on this forum using a bleach solution, namely 1/4 cup per 10 gallons.

Our process is:

Dump antifreeze
Fill with sanitizing solution, 1/4 cup per 10 gallons (1/2 cup for our 23)
Bring Hot Water heater back in the loop to sanitize
Run the boat for an hour
Dump the bleach water
Fill with rinse water
Dump the rinse water
Fill the tank.
 
We also use an inline filter, with a charcoal component, when filling the tank as well as an in line filter, again having a charcoal component, 3M made, before the pump. The Admiral says it tastes better than bottled filtered water! I have to agree.
 
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