Boondocking Basics

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How to Sanitize an RV Fresh Water Tank

How to Sanitize an RV Fresh Water Tank


Sanitizing an RV fresh water tank is pretty easy to do, you just need some common household bleach, a lot of water, and a garden hose. You’ll need access to an outdoor water faucet too. Don’t worry if the water you’re using is potable or not. The bleach will take care of that.

how to sanitize rv water tank
Dumping at Sawtooth National Recreation Area, Ketchum, ID

How to Sanitize an RV Fresh Water Tank

Pour one full cup of liquid household bleach into your fresh water tank for every 50 gallons of tank capacity.

  • So, if your tank holds 100 gallons of water, use 2 cups. If your tank holds 25 gallons, use a half-cup.
  • Fill your tank completely full of water.
  • Let sit for at least 8 hours.
  • After 8 hours, you can either drain the water from the tank’s drain exterior valve, or better yet, run all the water faucets, including the shower and toilet, to pull that sanitizing solution through your RV’s water lines. Then drain both the gray and black tanks.

Do I Have to Completely Drain the Tank Before Sanitizing?

Actually, you don’t have to. It’s not really necessary. If the point is to completely kill everything in the tank, then why drain the tank first?

Just make sure you get the recommended amount of bleach in there.

How to Get Bleach Into Your Water Tank

Most people do it by pouring it directly into a garden hose, and then connecting the hose to the RV and water faucet, and turning on the water.

  • Use a small funnel to help pour bleach into the hose.
  • If your RV comes with a gravity-fill water port, you can just pour bleach directly into that. Make sure however, to follow that up with enough water to completely wash the bleach down through the fill pipe.
  • Many RVs come with a winterizing system that can suck water from a bucket and pull that into the water tank and water lines. You can certainly use this. However, this requires adding extra bleach just to make sure you’re getting the minimum amount required into your water tank.

How Do I Remove All of the Bleached Water From My Water Tank?

The best way is to run your faucets and leave them on until they start sputtering. That’s when you’ll know your water tank has emptied. While you’re running faucets, also run the shower and even run the toilet for several minutes too. Doing this will pull the solution into all of your water lines.

You can also open the drain valve on your water tank. All water tanks have a valve located at the bottom of their tank. But, we don’t recommend this. It’s better to pull that solution through your lines.

Should I Run the Hot Water Faucets Too?

Sure, absolutely. The only benefit is to pull sanitizing solution through the water lines delivering hot water. Otherwise, your water heater tank already keeps itself sanitized.

However, make sure to shut off your water heater first, and run the hot water faucets until all hot water is gone. When you boil bleach, it creates chlorine gas which will burn your eyes and mucous membranes. It will also create sodium hypochlorite which can damage the water heater tank.

How Often Should I Sanitize My Water Tank?

A good rule of thumb is once every six months. Fill up a clear glass with water and hold it up to the light to see if it looks hazy, yellow, or green. That’s how you will know. If the water looks white, then it sit for a minute; these are just tiny bubbles created by your water pump. You can also try tasting the water if you’re brave enough.

If any part of your water tank receives direct sunlight, you’ll want to sanitize the tank immediately after you pack up camp and leave. Direct sunlight causes algae to grow, and if you don’t stop algae right away it will completely take over your tank. If the design and location of your water tank is such that it often gets direct sunlight, then you MUST cover up that section of your tank with Reflectix sheeting (see it on Amazon) or some other light-blocking material.

Will it Hurt My RV If I Use Too Much Bleach?

Nope. If you get sloppy and pour too much bleach, don’t worry. It won’t hurt your RV at all.

There are some people out there who claim that using too much bleach will damage the seams on a water tank. However, we’re pretty certain that bleach does not damage the seams on the plastic jug that it comes in. I remember growing up and seeing the same bottle of bleach sitting above our washing machine for months without leaking.

And we’re only talking about letting the solution sit in your tank for 8 hours. Read more about, “How Much Bleach To Sanitize an RV Water Tank?

What if I Let the Solution Sit For More Than 8 Hours?

That doesn’t seem hurt anything either. Again, we’re not talking about filling your tank with pure bleach. We’re only talking about 2 or 3 cups at most, and the rest of it water.

We have personally poured more than that in our water tank, and our RV holds 100 gallons of water. In our years of full time RVing, we have not had a leak or crack in our water tank.

But Isn’t it Bad to Flush Sanitizing Solution Down the Toilet?

Yes and no. If you held down the pedal on your RV toilet to draw sanitizing solution through water lines, the small amount of bleach solution could kill off some beneficial bacteria in your black tank. However, once you drain the contents of your black tank, your bacteria colony will quickly recover and return your black tank’s “environment” back to ideal.

If you’re concerned about mixing bleach with the ammonia that naturally occurs in urine, yes technically that can create chloramine gas, which is deadly to humans and pets. However, we’re only talking about a very small amount of bleach. Moreover, all black tanks come with a vent that allows chloramine gas to escape through your RV’s roof, and not into your living space.

There’s Still a Small Puddle of Sanitizing Solution Remaining in My Water Tank

Once you’ve pumped out as much as sanitizing solution as you can from your water tank, certainly there will be a small puddle remaining.

This is why we use bleach. When bleach is diluted with water, it’s still safe for people and pets to drink. Just refill your tank with clean water, and it’s highly unlikely you’ll even notice the tiny amounts of bleach left behind. Yes, there are some people who claim that consuming small amounts of bleach is dangerous, or will cause cancer… But, if you’ve ever swam in a swimming pool, then you’ve already absorbed quite a bit of bleach.

If it still bothers you, then just completely drain the water tank and refill with fresh water over and over again until you’ve diluted the bleach down to a point where you’re comfortable with it.

Can I Use Something Other Than Bleach?

Vinegar – Some RVers use white vinegar. However, it takes a lot more vinegar. Most RVers recommend a 50/50 mixture of vinegar to water. Obviously, this is only feasible with small water tanks, perhaps 20-gallons or less. You will also have to leave it sit for much longer. Moreover, vinegar is not enough to kill off all bacteria. There are still some strains that survive it. However, you can still kill them by using heated vinegar. To do this, you will have to fill your water tank with hot water, at least 130 degrees F or higher. This is not going to be easy considering most RV water heaters are only 6 to 10 gallons in size.

Baking Soda – Some people recommend sanitizing with baking soda, but this is not an effective way to kill pathogens. You will also need a 50/50 mix of baking soda to water. It’s very difficult to get that much baking soda into an RV water tank. Also, when water mixes with baking soda, it creates carbon dioxide gas, and the creation of that gas will cause the sanitizing solution to bubble out of the overflow valve of your water tank. You will also have to make sure no clumps of baking soda remain in your tank, otherwise it will get sucked into the water pump, and get clogged up.

Hydrogen Peroxide 3% – This is an effective way to kill off most bacteria, but still not all. Moreover, you must use only pure Hydrogen Peroxide 3%, and not add any water. This is only feasible with small water tanks that you can remove, open up, and wash by hand.

What About Using Sanitizing Tablets?

You can certainly use sanitizing tablets. The challenge is getting them inside your water tank. If your RV has a gravity-fill system, you can try dropping them in there and then flushing it down with water until they’ve completely dissolved. Another way is to shove them into a garden hose, connecting up the hose to your RV, and running water.

Not all sanitizing tablets are equal however. Some kill off only certain types of bacteria, while others kill off everything. For more information read, “Using Water Purifying Tablets for RV Use“.

How to Sanitize Your Water Tank While Boondocking

To be honest, this is not something you want to do while boondocking. The reason is that you need to completely fill your tank with bleached water and let it sit for at least 8 hours and then drain it all. The best way to do this is when you’re hooked up to water and sewer.

If you absolutely don’t want to pay to park overnight, then try this instead…

  • On the day you pack up camp and drive out, stop at an RV dump station, preferably in the morning.
  • Fill up your water tank with sanitizing solution.
  • Then, spend the next several hours driving to another dump station.
  • When you get there, hook up your sewer hose, and run your water faucets and let them drain into your gray and black tanks until empty.
  • Then refill your water tank with clean water, and you’re done.
  • If you can manage driving for 8 hours, this works pretty well. If you can only drive for 3 or 4 hours, then try tripling the amount of bleach.

Is it Safe to Dump Bleached Water Into an RV Park Sewer?

For the most part, yes. As long as the RV park is connected to a city or county sewer system, there’s no problem with it. However, there are some RV parks located in rural areas that drain into a septic tank. In this case, the RV park does not want guests dumping bleach, formaldehyde, or other chemicals into their septic because it kills off the bacteria that breaks down solid matter. But there are many other rural RV parks don’t seem to care. Before you book a night at an RV park, you may want to ask if it’s OK to dump your gray and black tanks containing bleach.

The Water in My RV Water Tank Still Tastes Nasty After Sanitizing

This biggest reason for this is the plastic tank. When water sits in a plastic tank or Pexate pipe for several hours to several days, it just doesn’t taste all that great. It’s a bigger issue when you have a larger water tank, and it takes 3-4 weeks to use it all.

This is why many boondockers don’t drink from their water tanks. They only use it for showering, washing dishes, flushing toilets, cooking, brushing teeth, or giving it to the dog. Otherwise, they drink from jugs of distilled water they’ve bought at the store or filled from some other water dispenser.

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1 thought on “How to Sanitize an RV Fresh Water Tank”

  1. One of the main tasks for progressing is to identify the RV fresh water tank drain valve location and release the drain plug.


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