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Sanitizing Question


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Greetings all.  In all my years of owning RV's, I have never had the opportunity to "sanitize" a water system.  We always just emptied out the fresh water, blew out the lines, and stored the unit for the winter.  Then added water in the Spring.  Regardless of rig, the water always tasted like it came from a plastic milk jug.  That's just the life of an RV'er.

Now we have a "new to us" '04 Holiday Rambler that was stored for years with water in it.  Yes, it froze.  About a dozen fittings, valves, lines, faucets, spigots, vacuum breaks, filters, toilet, and water pump all starting leaking (understatement) as soon as I put pressure to the system.  What a mess.  I just spent the last month sealing up all the leaks and fixing/replacing things.  It's tight now, and everything works as it should.  But since the coach was neglected by the previous owner, I want to go the last mile and "sanitize" the water system before I let my family drink any water from it.  So my question is this - the "book" says "to sanitize, put the hot water heater in bypass mode and then pour in 4 gallons of bleach infused water and run all the spigots".  Why "bypass mode" on the heater?  Don't nasty things grow in the hot water heater tank too?  Seeking advice.  I know I should (and will) flush the hot water heater tank.  But this won't kill any bacteria in it.  I can't think of any reason to close the "bypass" valve when sanitizing.  But I can think of a reason to leave it open during the process.  Will I hurt anything?  Thoughts?



Afterthought edit - It just occurred to me that the hot water heater holds 10 gallons and the fresh water tank holds 60 gallons.  The instructions say to use 1 gallon of water for each 15 gallons the water tank holds.  Then add 1/4 cup bleach to each resulting gallon and pour into empty holding tank.  This adds up to 4 gallons of water and 1 cup of bleach.  But this isn't taking into account the 10 gallons of fresh water in the water heater.  But if you put it in bypass mode, it won't matter.  Hmmmmm.....

Therefore, if I drain the hot water heater before the operation, the 4 gallons of sanitized solution will be immediately pumped into the hot water heater and there won't be any left to circulate through all the spigots.  If I don't empty the hot water heater prior to the operation, the mixture will be weak (14 gallons of water to one cup of bleach).  But if I put the water heater in bypass mode, I avoid the problem altogether.  Perhaps this is why they say to put the hot water heater in "bypass" mode for the sanitizing operation.

Edited by CorinthWest
May have answered my own question
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FYI It’s a water heater. Hot water doesn’t need heated 🤪

I think you’re going to get it sanitized with the process. Just be sure to drain and fill your tanks at least twice with fresh water to clean out the bleach. Bleach is also rough on rubber seals. Don’t leave it in there very long.

Jim 2000 Dynasty 

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Fasthobie16 -  Yeah, I'm sure the family will complain if they taste (or smell) chlorine.  Will rinse thoroughly.  Excellent advice.

Gary - I am aware of this phenomenon.  Good advice.  I learned this the hard way in our house water heater eons ago.  They don't call them "immersion heaters" for no reason.  LOL

Thanks, guys.

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I wrote this article a few years ago but it is still applicable. Good Luck.

If your fresh water tank develops an odor from algae or bacteria, you will need to clean it—otherwise it will simply get worse. Sorry, there is no quick-fix nor magic cleaner that I know of. Interestingly, one of the major causes of this problem is non-use. Many RVers simply don’t use the water in the tank and, after some time, it will go bad (just like the milk in your fridge). The time it takes for the water to start to go bad (develop odors, taste bad, etc.) is affected by heat (hot weather will enhance bacteria growth), non-use (water just sits in the tank), and filling the tank with “questionable” (untreated) water.

Where Does the Water Go?
When you hook up your white water hose to the “campground” water connection and your RV and turn the faucet “on,” you will either put water into the fresh water tank OR it will bypass the tank and go directly to the faucets inside the RV. On some “expensive” or “high-end” RVs, there is a switch that allows you to use water from the fresh tank while automatically keeping that tank full. However, this is the exception! On most RVs, it’s water FROM the tank or AROUND the tank.

The RVer may park in the campsite, hook up the water, and assume everything is fine. Oddly, it is. The water in the RV will work just fine. The problem is that the water in the fresh water tank is not being used.

There is also a common misconception among newer RVers that they can flush their fresh water tank by simply hooking up to any water supply and turning on the faucets inside the RV. The only way to actually use water from your fresh water tank is to have the external water shut off at the external source (campground water faucet) and use the water pump in the RV. So, you cannot simply “flush” their fresh water tank by running fresh water through the system.

Disinfecting your Fresh Water Tank
There is a definite process to clean your fresh water tank and it’s neither fast nor easy. Sorry! So, for those RVers that think they can just dump a little bleach into their tank and “all is good,” this may be a surprise. Plus, unless you do it thoroughly, the odors and bad taste will likely return.

To clean your fresh water tank, use some chlorine bleach, and do this…

  1. Drain and flush out the fresh water tank a couple of times.
  2. Remove any water purification equipment and water-filter cartridges.
  3. Use 1/4-cup of liquid household bleach (sodium hypochlorite) for every 15 gallons of fresh-water tank capacity. It’s easy to mix this in a gallon jug.
  4. Pour the solution directly into the fresh water tank. Most RVs have a gravity fill. You can pour it in there. If there is no handy gravity fill, get a short length of water hose, attach the end to your RV water fill connection, and use a funnel in the other end. Pour the bleach solution into the funnel.
  5. Fill the tank with fresh water.
  6. Drive around—preferably on bumpy roads. You want to cause the bleach solution to slosh all over the inside of the fresh water tank including the inside top of the tank. Just sitting there the bleach won't reach the upper insides of the tank.
  7. Turn on the water pump and all faucets to pump the bleach-solution through the system to every hot and cold faucet at every sink, shower-head, into the toilet, water heater, and don’t forget external faucets. You should smell the distinct odor of bleach (chlorine) at every fixture.
  8. Close all the faucets and turn off the water pump.
  9. Let the bleach solution remain in the system for 2–4 hours.
  10. Drain and flush the system. Top off the tank with fresh water and go for another drive (to splash around and wash out the residual bleach). Fill and drain and drive and splash until there is no more bleach odor.

[Author Note… Keep in mind that many/most campgrounds will not allow you to fill and dump full tanks of water at a campsite. Finding a location that will allow you to complete this flushing process may be challenging.]

NOT An Alternative Solution
There is much rumor and myth in the RV world that you can disinfect a fresh water tank using hydrogen peroxide (the stuff you can buy off-the-shelf at the store). The bottle of 3% hydrogen peroxide that you likely have in your RV or house won’t do the job—it is not a strong enough solution. Even if you could fill the fresh water tank with the 3% hydrogen peroxide, it wouldn’t do the disinfecting job you need.

The higher concentrate required to complete the disinfectant is only sold to authorized recipients—chemical companies, school systems, industry, etc.—and is only available at chemical-supply houses. That concentrate may be as high as 50%—significantly stronger than the off-the-shelf bottle available at your local store. Plus, when using the highly-concentrated solution, there is a specific process required to neutralize the level of hydrogen peroxide after disinfecting to make the tank safe for normal usage. I won’t go into that process here.

So, just disregard the rumor about cleaning your fresh water tank with hydrogen peroxide.

A Different Solution
The most simple and easiest method to avoid having to clean or disinfect the fresh water tank is to use that water regularly. Even if you are hooked up to the campground water supply, get in the habit of using the water from your fresh water tank (shut off the campground faucet and turn on your water pump), and then refill the tank as needed. You do not have to put your hose away to accomplish this.

It is the exact same process as camping in freezing weather… you fill up the fresh water tank, disconnect the water hose, okay, you do have to put it away in the winter (to keep it from freezing), and live out of your fresh water tank. When your tank gets low, get out the hose, and fill the tank again. You can do this indefinitely.

Since we boondock regularly—we averaged 12 nights per month for the last few years AND have fulltimed going on 20 years now—we normally use the water from the fresh water tank. Therefore, our fresh (on board) water is regularly used up and refilled. Boondocking is sort of an automatic method of forcing you to use that fresh water. The good news is that we have never needed to disinfect the fresh water tank.

Use any process that forces you to regularly use the contents of the fresh water tank. Fulltimers and those who do lots of boondocking go for years without experiencing fresh water tank odors or problems. We also never needed to disinfect the tank for over eight years in our previous coach.

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Kevin/Ron - WOW.  "Ask and ye shall receive".  Thanks guys.  Some of what you posted looks like it came out of my Holiday Rambler Owner's Manual, because it's almost exactly the same.  But your advice is appreciated.  Since you have both done this before, what do you guys do about the Water Heater bypass valve?  Open or closed?

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I’m not sure I have Aqua hot system. No hot water tank. A friend of mine has a small camper. He sanitizers his the same way I do. Just runs the hot water until he smells bleach and let it sit for four hours and then flush is it all out. I am not sure if that’s right or not but that’s how he does it .

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No water heater - we had an AquaHot.

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