We get asked all the time: Do we flush, clean or sanitize freshwater tanks? No, not as a part of our service, but we’re happy to go over the process — something every RVer should know how to do — with anyone that asks.

For our own RV, we sanitize it every spring when we de-winterize, usually once or twice during the year (depending on usage), and anytime we notice an odor in the RV water system. The process is actually quite easy, though it does take some time, to plan accordingly. We’ll go through the process if you are during this as a part of your de-winterizing as well as mid-year.

Why You Need To Sanitize Your Water Tank
RV fresh water tanks are manufactured from food-grade FDA-approved, virgin polyethylene plastic resin. This material is safe for fresh drinking water storage, yet strong enough to handle the rigors of a moving RV.

A sealed water system, over time, will begin to accumulate slime and algae. This is especially true if you don’t know the condition and properties of the water you take onboard at different parks and stops. Some parks, especially state and national parks, dispense well water, which can be cloudy with sediment, minerals or other particles in it.

This is just one reason why it is critical to use a filtering system, whether the common blue, disposable inline canisters or a more expensive filter and softening system with multiple filtering methods.

Caring For Your Fresh Water Tank
First, only use the white, non-toxic water hoses that specifically state for use with RV fresh water systems. We like to have two lengths with us at all time. Never use these hoses for anything you would do with your RV’s waste system in any manner. Other types of hoses, like common garden hoses, can leach chemicals into your water supply.

Second, a filtration system is absolutely critical. The filter will keep debris from entering your water storage tank or freshwater system (if used directly and bypassing your freshwater tank). Some filter systems can even remove some bacterias and even lead. Be sure to check your system’s manufacturer’s guidelines and follow all recommended maintenance schedules, such as regular cleanings and replacement of filter cartridges.

Finally, keep your RV’s water storage tank clean and sanitized. As we mentioned, at a minimum, this should be done once a year when you take your RV out of storage, perhaps when de-winterizing and getting ready for the new RVing season.

Mid-Season Sanitizing
If you’re mid-way through your RVing season (or maybe you RV full-time), you’ll need to take a couple of extra steps before you actually sanitize your tank. You ant the fresh water system to be completely empty.

Obviously, your first step is to disconnect the park supply of water to your RV. You don’t want the system refilling as fast as you are emptying it!

Next, drain the water heater tank. Make sure the water in the tank is not hot (turn off the heating system and run the hot water through the kitchen or galley tap until the water is cold or at least cool). Again, make sure to turn your water heater off. Otherwise, it will fire up and try to heat water as it is being emptied. You also NEVER want to drain your water heater tank with the heater element turned on. This will burn out the element in just a few seconds.

Once the tank’s water is cold or cool, release the pressure relief valve and then open the drain plug, or petcock, usually located in the bottom, left corner of the water heater tank (when you have opened the access door on the side of your RV). This will allow the tank to empty of water.

This is also a great time to use a water heater wand to flush out your rank of sediment that has collected at the bottom of the water heater tank. If your RV’s water heating tank has an anode, examine it and replace, if necessary. Replace the drain plug and close the pressure release valve. Do NOT turn on the heating element.

Next, locate the low-point water drains and open them so that the water in the system can drain completely.

Finally, find the fresh water tank and drain the water in it. Use the water pump to force all of the water out. When water stops coming out of the tank, turn the pump off or it may get damaged. Close all the drains when you are done.

How To Sanitize
The process is actually to sanitize your tanks from this point on. What you want to do is fill your fresh water holding tank with a mixture of bleach and water. The amount of bleach depends on the capacity of your freshwater tank:

  • 15-gallon tank: one cup of bleach
  • 30-gallon tank: two cups of bleach
  • 45-gallon tank: three cups of bleach
  • 60-gallon tank: four cups of bleach
  • 75-gallon tank: five cups of bleach
  • 90-gallon tank: six cups of bleach

You get the idea. Basically, the ratio is one cup of bleach for every 15 gallons of water. Best to be a bit liberal in your measurements if your RV’s fresh water tank falls in between these measurements. For instance, a common freshwater tank capacity for larger motorhomes is 100 gallons. For this size, we’d use seven cups of bleach.

A lot of RVers wonder how to get the bleach into the holding tank. We suppose you could use a funnel or something similar, but there’s a better way. You’re using your white water hose to fill your holding tank, right? Before you turn on the water to fill the tank, pour the amount of bleach needed (see above) into the white hose, place the hose nozzle into your freshwater input (or attach it, if you wish), and then turn the water on to fill your holding tank. That’s it! Easy, huh? And no bleach to splash onto your shirt or pants, much less the ground or your RV.

Once your RV’s fresh water tank is full (watch your sensor panel), open up each of your RV’s water faucets a bit until you smell the bleach. Make sure to open the gally, bathroom, shower/tub and any outside faucets you may have. You want them open only enough to smell the bleach.

Next, you wait. Some may say you need to only wait a few hours, letting the bleach in your fresh water tank and water system do its job. We like to leave everything to sit for at least 12 hours, if not overnight.

After the waiting period, turn on all faucets in your RV, letting your fresh water system pump force all of the water out of the holding tank. When water stops coming out of the tank, turn the pump off or it may get damaged. If your holding tanks are full, now would be a good time to empty them into the sewer.

Refill your fresh water holding tank again, this time without the bleach. There’s no wait this time — just turn on all faucets in your RV, letting your fresh water system pump force all of the water out of the holding tank. Repeat these last two steps — refilling the fresh water tank and then emptying it — until you no longer smell the bleach. This may take two or even three cycles of filling and emptying.

When De-Winterizing
If you’ve properly de-winterized your RV, you know the water system is completely empty, or, at the very least, contains a small amount of RV-type antifreeze (the most common type is the pink stuff). This is the easiest time to sanitize your RV’s fresh water tank. Proceed with the steps outlined above, under How To Sanitize.

Your RV’s fresh water holding tank is now clean and sanitized. As we said, we like to do this when we are de-winterizing as well as once or twice during the RV season or when we feel the water is stale and maybe a bit smelly. At the very least, we would do this twice a year if your RV full time and use your holding tank often. Even if you only ever use RV park water, we would still recommend a sanitize once a year.