% bleach to sanitize fresh water tanks

[rvshrinker]

First time doing this chore.

Most sources say to use household bleach 1/4 cup for every 15 gallons of fresh water capacity. Mix required bleach amount in some fresh water, pour into your tanks, fill with potable water, let sit, drain, rinse.

However other sources say 1/4 cup for 10 gallons.

For a 60 gallon freshwater tank, this is either 1 cup or 1.5 cups of bleach.

But according to this fact sheet from the Northeastern University Dept of Environmental Health Sciences, bleach should be concentrated at 5000 - 20,000 ppm to disinfect. 5% bleach is 50,000 ppm, 10% bleach 100,000 ppm, etc. This would imply diluting 5% bleach no more than 10:1 to get to a concentration of 5000 ppm, the minimum for disinfecting. Then the 60 gallon tank needs ~5 gallons of 5% bleach and 55 gallons of water to be diluted properly for disinfection.

That’s a big difference.

https://www.northeastern.edu/ehs/wp-content/uploads/2014/12/Bleach-Fact-Sheet-Draft.ejc2_.pdf

And this Idaho DEQ website says dilute 1000:1:

https://www.deq.idaho.gov/media/517665-disinfecting-water-wells-storage-tanks-fact-sheet-0612.pdf

What is the correct concentration of bleach to disinfect the water tanks?

[RoyF]

After draining the bleach, I suggest adding a cup or two distilled vinegar when you refill the tank. Drain again and refill with water only.

[GordonThree]

more is better doesn't really apply to the time it takes for bleach to do its job. as an oxidizer it needs a certain amount of time to breakdown the various organic barriers employed by microbes. so more doesn't mean faster sanitizing, it just means wasted time and water as you'll spend a lot more time rinsing it out.

Just what do you think has been growing in your tank over the winter anyway? are you planning to use a non-potable source, so the bleach not only has to sanitize the tank, but also the entire volume of water?

[opnspaces]

the minimum ratio will work, but it might need to soak for a long time. If you increase the ratio you cut the soak time. For instance my Jayco manual says take the tank capacity and multiply by .13. So my tank needs 5.2 oz of bleach. 40*.13=5.2

That will take 4 hours to disinfect. However if I double the bleach to 10.4 oz. My soak time goes down to 1 hour.

To add the bleach I hook the water hose to the trailer tank. Then I pour 1cup bleach into the faucet end of the hose and screw it onto the spigot. turn on the water and let the tank fill.

If I go with the standard 1/4 cup per 10 gallons I would add one cup (8oz) to my 40 gallon tank. This makes a stronger solution than the minimum (5.2 oz) without being so strong it damages the internal components. So most people will just take the easy route of saying 1/4 cup per 10 gallons over 4 hours.

Below is the excerpt from my owners manual.

Sanitizing the Potable Water System

WARNING: Failure to sanitize the potable water system could result in
death or serious illness.

1. Use one of the following methods to determine the amount of common household
bleach needed to sanitize the tank.
 Multiply “gallons of tank capacity” by 0.13; the result is the ounces of bleach
needed to sanitize the tank.
 Multiply “liters of tank capacity” by 1.0; the result is the milliliters of bleach
needed to sanitize the tank.
2. Mix the proper amount of bleach into a container of water.
3. Pour the solution (water/bleach) into the tank and fill the tank with potable water.
4. Open all faucets (Hot and Cold) allowing the water to run until the distinct odor of
chlorine is detected.
5. The standard solution must have four (4) hours of contact time to disinfect
completely. Doubling the solution concentration allows for contact time of one (1)
hour.
6. When the contact time is completed, drain the tank. Refill with potable water and
purge the plumbing of all sanitizing solution.
If there is a problem of excessive chlorine odor and taste after the sanitizing process, follow
the above procedures using a solution of baking soda (1/2 cup added to one gallon (4 liters)
of water per 15 gallons (60 liters) of tank capacity) or vinegar (one quart added to five
gallons (20 liters) of water per 15 gallons (60 liters) of tank capacity.)
Your demand water system is now ready for use. Refer to instructions on filling the tank
and utilizing the system in the “Setting Up Camp...” chapter

[Lwiddis]

Per the EPA at https://www.epa.gov/ground-water-and-drinking-water/emergency-disinfection-drinking-water

[Boon_Docker]

I have always used 8 oz of household bleach for my 30 gallon tank.

1000:1 sounds right. As per your link above.