I have received more than a few questions on my RV Dewinterization Basics video, where people have questioned the wisdom of allowing bleach solution into the metal hot water tank. Some people have asked genuinely concerned after seeing other videos, while others have not been so polite.
The line of comments generally goes something like this, “I like your video but disagree that you should put bleach into the hot water heater.” Others mention that they have seen content creators say that you should never put bleach in a hot water heater.
Being analytical by nature (and former career) and not seeing this prohibition in the RV manufacturer’s water system sanitation directions or the water heater manufacturer’s owner’s operation manual, I decided to investigate further.
With the help of a structural engineer I know from a specific RV forum, I was pointed to a metallurgy study of hypochlorite solutions (bleach solutions) and their effects on the weight loss of metals (corrosion) over time and at various dilution levels. This may get a bit technical, but it is essential to understand when weighing the actual vs. perceived risk of putting a bleach sanitizing solution into a metal holding tank.
The trade-off in terms of risk is corrosive damage to the hot water tank over time vs. the immediate health risk of not sanitizing the entire RV plumbing system, including the hot water tank. It is a risk trade-off that each of us with RVs who sanitize the plumbing systems should be aware of.
Here are the main assumptions and outcomes of the study applied to this issue, which show why I generally think a diluted bleach solution in a metal hot water tank for minimal time is not a critical issue for the life expectancy of the equipment.
Assumptions:
– RV manufacturers generally recommend a sanitizing solution of 1/4 cup household bleach per 15 gallons of water (1 part bleach per 960 parts water) or approximately 1,042 ppm (parts per million). This solution would remain in the plumbing system for a minimum of three hours to sanitize the system.
– The India Journal of Chemical Technology Study (Vol 1 July 1994)[1] shows that for this level of Chloride (see Table 1, pg. 226), the Corrosion rate would be approximately 3.32 mpy (thousandths of an inch per year) given exposure for one full year (8,760 hours).
– Household bleach is only about 5% Chloride, so the actual ppm would be closer to 200 ppm, yet the study doesn’t diminish the mpy much, so we will be conservative and keep the 3.32 mpy Corrosion rate for a full year’s exposure.
– Given an exposure of 3 hours, the mpy reduction factor would be (3 hr./8760 hr.) or .00034247. So, the study estimated 3.32 thousandths of an inch of surface loss if the solution sat in the tank for an entire year, yet the solution only sits for three hours. Therefore,
Conclusion:
The adjusted Corrosion rate would be the year-based mpy of 3.32 multiplied by the reduction factor of 3 hrs. (.00034247) to yield an adjusted mpy of .001137. This equates to 1.137 millionths of an inch of corrosion for three hours of exposure to a household bleach solution of 200+ ppm.
How thick is a millionth of an inch? It is not perceivable. If, for example, the interior metal wall of your hot water tank is 1/8th of an inch wide, it is .125″ in decimal form. 1.137 millionths of an inch is .000001137 in decimal form. To calculate how long the solution would take at this dilution level for this length of time (soaking for 3 hrs. per year) to corrode 1/8th of an inch of metal, you would divide .125 / .000001137 = 110,619 years. Your RV likely won’t be around by then.
According to my structural engineer friend, the real risk of corrosion to your hot water tank is not due to a diluted bleach solution used for a very short period. The real danger of corrosion lies in the water’s acidity level left in the tank during regular use. Most of us tend to leave water in the hot water tank during camping season and between trips. Few people drain all water from the plumbing system, including the hot water tank, between trips in-season (maybe we all should). Thus, the risk of leaving acidic water in a tank for prolonged periods. He mentioned that anyone could use a simple pool water tester to check the pH level of the water at your water source to see if this is an issue and add baking soda to the tank to add pH to acidic water.
Hopefully, if you have read this far, you at least understand why I do what I do. I simply am much more concerned with a sanitary plumbing system and staying healthy while using my RV vs. the long (or very long) term effect of corrosion on my hot water tank. One trip to the emergency room today would likely pay for multiple replacements of a hot water tank.
If you would like to study the Metallurgy paper referenced and learn more, here is the link to the article.
As always, I encourage you to consult the specific manuals pertinent to your RV when performing any service.
All the best in your camping endeavors!
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