RV HOLDING TANKS need to be properly maintained for you to enjoy camping to the fullest. Most RVs have three holding tanks for fresh water, gray water, and black water. Only one is responsible for providing safe water for drinking, showering, and washing dishes: your fresh water tank. To ensure it does that, you’ll need to learn how to sanitize an RV fresh water tank, how often to do it, and the different methods you can use.
RV technicians at any Camping World Service Center can perform this important RV maintenance task for you. But here’s how to do it on your own if you feel comfortable.
When To Sanitize an RV Fresh Water Tank
Some manufacturers recommend sanitizing your fresh water tank “after each use,” but this is interpreted in two ways. Most RVers sanitize their fresh water system each year, usually in the spring when they dewinterize their RV to prep for spring camping.
Others perform this task whenever their RV has sat unused for 2-4 weeks. Either way, this routine maintenance task guarantees safe water for drinking, showering, dishwashing, and laundry on the road. It doesn’t require special tools; you can do it with bleach or a more environmentally friendly cleaning solution.
Technician Tip: If you’re reading this before storing your RV for the season and want to know how to winterize it, read our tutorial on RV winterization.
Supplies for Sanitizing an RV Fresh Water Tank
You can always bring your RV into a Camping World Service Center to have your potable water tank sanitized, but the process doesn’t require any special tools.
Here’s what you’ll need:
Technician Tip: As long as it’s mixed with the correct amount of water to obtain the right ratio, bleach is safe for all the components of your RV’s water system, including the water pump.
Sanitizing an RV Fresh Water Tank with Bleach
Before draining your fresh water system, park your RV where water will percolate into the soil or run downhill safely. For example, don’t do this in an RV park if the slope will create a pool of water in your neighbor’s site. Because you’ll eventually be flushing bleach or a cleaning solution out of your water system, your best choice is to park where you can access a sewer connection and a fresh water source.
Follow these step-by-step instructions to sanitize your RV’s entire fresh water system:
Step 1: Turn Off Your Water Heater and Water Pump
Draining your fresh water system with the water heater on can damage the tank. Turn off your water heater and run hot water for a minute or so to flush out the heated water before draining it. Running hot water for 1-2 minutes should be enough to flush the tank and allow it to cool before draining.
This is also the time to ensure your water pump is turned off. Opening all the faucets in your kitchen and bathroom will allow air to naturally help drain water from your fresh water system (similar to removing the cap on a car’s oil inlet before draining the oil). Then, open the pressure relief valve and remove the plug or anode rod to drain the water heater tank. This is a good time to inspect your anode rod and replace it as recommended by the manufacturer.
Make sure your gray water holding tank is empty before continuing. If you’re in a good location to do so, you can set up your sewer connection to easily empty your RV holding tanks when the time comes.
Step 2: Drain The Fresh Water
Skip to step 3 if your tank is already empty because you drained it when winterizing your RV.
Locate the fresh water tank drain and low-point drains for your RV’s plumbing lines underneath your coach. Most RVs have a drain directly underneath your fresh water tank. Some have multiple drains for the cold water system, depending on the locations of the low points in your coach’s plumbing.
These drains are sometimes easy to identify by red (hot water) or blue (cold water) drains coming out of the bottom of your RV, but some manufacturers use white or opaque PEX. Consult your owner’s manual if you’re having trouble locating these drains on your RV. Once you’ve located them, open the low-point and tank drains to use gravity to drain water from your fresh water tank, plumbing lines, and hot water tank.
Technician Tip: Now is a great time to check your fresh water tank’s hose clamp on the filler tube. This clamp must be tight before your fresh water tank is filled, and it can sometimes be left loose on new RVs. You’ll find this clamp on the side of your fresh water tank closest to the fill inlet. On some travel trailers, the water tank will be in an underneath storage compartment, or it may be located under the bed of smaller trailers.
Step 3: Measure and Add Bleach
While your system is draining, calculate how much bleach to sanitize your RV water tank. You’ll need about 1/4 cup of bleach for every 16 gallons of water in your fresh water tank. Another helpful ratio is to use one ounce of bleach for every eight gallons of fresh water. Based on these ratios, measure the appropriate amount of bleach for your RV. For example, if you have a 20-gallon fresh water tank, you’d need roughly 2.5 ounces of bleach to sanitize your system.
With your bleach measured, go back and check on those low-point drains. Close them when the water stops draining. STOP! Don’t add the bleach straight to your fresh water tank. Dilute it in at least a gallon of water, then use your funnel to pour the bleach mixture into the fresh water inlet on the side of your RV.
Technician Tip: If your RV has an overfill vent on the fresh water inlet, you may not be able to pour in bleach solution using a funnel. In this case, pour the solution into your hose and hook it up to a water source to get the bleach into your tank.
How Much Bleach Do I Need? (Quick Reference by Tank Size)
| Tank Size (gallons) | Bleach Needed (cups) | Bleach Needed (ounces) | Notes |
|---|---|---|---|
| 20 gal | ~⅓ cup | ~2.5 oz | Typical small travel trailer |
| 30 gal | ~½ cup | ~3.75 oz | Common mid-size trailer |
| 40 gal | ~⅔ cup | ~5 oz | Common mid-size trailer |
| 50 gal | ~¾ cup | ~6.25 oz | Common Class C / 5th wheel |
| 60 gal | ~1 cup | ~7.5 oz | Class A / large 5th wheel |
| 80 gal | ~1¼ cup | ~10 oz | Large Class A |
| 100 gal | ~1½ cup | ~12.5 oz | Large Class A motorhome |
Ratio: 1/4 cup (about 2 oz) of bleach per 16 gallons of fresh water capacity.
Step 4: Fill the Tank with Potable Water and Pump It Through The System
The next step is to fill your tank with clean water. Connect your water hose to a fresh water connection and fill your tank completely so that the bleach dilution mixes throughout.
Once your tank is full, replace the cap on your fresh water inlet. Next, circulate the bleach solution throughout the plumbing lines. Go inside your RV and turn on your water pump. Then open all the faucets and showerheads and run the bleached water through every part of your fresh water system for 2-3 minutes. It’s okay to have a trace amount of bleached water in your gray tank for 12-24 hours, but no longer. Once the water has circulated for several minutes, you can close the faucets and shut off your water pump again.
Technician Tip: You may also consider using an RV water filter when filling your tank to use the cleanest water possible when sanitizing your tank.
Running the bleach solution through all your faucets also sanitizes your RV’s water lines — not just the tank. This is why it’s important to open every faucet and showerhead in Step 4, rather than just running the pump.
Step 5: Let It Sit Before Draining
Proper tank sanitization doesn’t happen immediately. Let your mixture of clean water and bleach sit in your tank and plumbing lines for 12-24 hours before draining it. If you start this process in the afternoon, just let it sit overnight and come back in the morning.
Technician Tip: WARNING! Don’t let the bleach mixture sit for more than 24 hours.
After at least 12 hours (but no more than 24), it’s time to drain the system. Your best bet is to have full hookups for this process. If you’re using bleach, it’s recommended to avoid draining your tank into the soil, as it can harm plants and degrade soil health.
One solution is to place a five-gallon bucket or a portable RV holding tank under your low-point valves to collect your bleach mixture and dispose of it into an appropriate sewer inlet, such as those at RV dump stations. But the best option is to turn on your water pump, open all your faucets (including the shower), and let the water flow through the system into your gray water tank, provided you’ve already hooked it up to a sewer connection.
If you run your bleach mixture through your plumbing system and into your gray water tank, it’s still best to open the low-point valve after you shut off your water pump. This allows your fresh water tank to drain completely and prevents a small amount of water and bleach from getting left behind. Another option is to drain them the same way you initially drained your tanks to prepare for sanitization. Open the low-point valve (or valves) and allow the water to drain completely. However, you should only do this if you are using an environmentally friendly cleaner (i.e., not bleach).
Technician Tip: Bleach and rubber aren’t best friends, so don’t let this solution sit in your gray holding tank. But running it through as you flush the system isn’t likely to cause damage and can also partially sanitize your gray tank simultaneously.
Step 6: Flush The System
Your final step is to refill your tank with fresh water and circulate it through the system with your water pump. Open all the faucets and flush the system until you can no longer smell the bleach. At this point, you can leave the handle for your gray water tank open so the system remains open as you flush the remaining bleach solution.
You may need to refill the tank and flush it several times until the smell of bleach is long gone. This ensures you have eliminated all sanitizing chemicals from the system and are ready to use the water in that tank again.
After you’ve replaced those filters, you should be ready for another full year of camping. If you’re not heading out for a trip immediately and overnight temperatures will stay above freezing, leave your tank empty until you actually need water inside your RV.
Technician Tip: If your RV is equipped with an onboard water filtration system, installing replacement water filters after sanitization is a good idea. Learn more about RV water filtration systems.
How To Sanitize an RV Fresh Water Tank Without Bleach
If you don’t want to use bleach, there is a more environmentally friendly way. The process is nearly identical to the bleach method above — follow the same six steps, with these differences:
Step 1: Turn Off Your Water Heater and Water Pump
Same as the bleach method. Turn off your water heater, run hot water for 1–2 minutes, turn off your water pump, open all faucets to allow draining, and open the pressure relief valve to drain the water heater tank.
Step 2: Drain The Fresh Water
Same as the bleach method. Locate and open your fresh water tank drain and low-point drains, and allow the tank to empty completely using gravity.
Step 3: Measure and Add Your Sanitizer
This is where the process differs. Instead of bleach, you’ll use an RV-approved, biodegradable fresh water tank sanitizer. Make sure any product you choose is approved by your RV’s manufacturer.
Our top picks:
- Thetford Fresh Water Tank Sanitizer Kit — A two-part system that cleans and sanitizes simultaneously. Follow the package directions for the correct amount per gallon of tank capacity.
- Camco TastePure Water Freshener — Reduces odors and improves taste. Note: TastePure is a cleaner, not a sanitizer. It will not kill bacteria on its own and is best used as a follow-up after a full sanitization cycle.
Once your system has finished draining and you’ve closed the low-point drains, dilute your sanitizer according to the manufacturer’s instructions. Pour the mixture into your fresh water inlet using your funnel.
Technician Tip: Non-bleach sanitizers are generally safe to drain directly onto the ground, but always check the product label to confirm. This makes them a great choice when you’re camping without sewer hookups.
Step 4: Fill the Tank with Potable Water and Pump It Through The System
Same as the bleach method. Connect your hose to a fresh water source and fill the tank completely. Turn on your water pump and open all faucets and showerheads to circulate the sanitizer solution through every part of your fresh water system for 2–3 minutes, then close the faucets and shut off the pump.
Step 5: Let It Sit, Then Drain
Soak time varies by product. Check the manufacturer’s instructions rather than defaulting to the 12–24 hour bleach window. Some RV sanitizers require as little as 15 minutes; others recommend several hours.
Once the soak time is complete, drain the system. Unlike bleach, most biodegradable sanitizers are safe to drain directly into the soil, but confirm this on the product label before doing so. If in doubt, collect the solution in a five-gallon bucket and dispose of it at an RV dump station.
Step 6: Flush The System
Same as the bleach method. Refill the tank with fresh water and circulate it through all faucets and showerheads until the water runs clear and you can no longer detect any sanitizer odor. Non-bleach sanitizers typically require fewer rinse cycles than bleach.
What Is the Best RV Fresh Water Tank Sanitizer?
TastePure Spring Fresh is a cleaner but not a sanitizer. It helps with odors but may not kill parasites or bacteria. If you’re looking for a complete fresh water tank sanitizing solution, we recommend checking out this all-in-one Thetford sanitizing kit. It’s an easy two-part system that cleans and sanitizes your fresh water tank and removes harmful bacteria, so you can enjoy safe water on all your upcoming RV adventures.
Make sure any RV fresh water tank sanitizer you choose is approved by your RV manufacturer. Follow the instructions carefully to use the correct quantity for the size of your fresh water tank.
For another pre-mixed option, look for the Star Brite AQUA™ Water Tank & System Flush. It’s a ready-to-use bleach-and-water solution — just pour in the correct amount for your tank size and follow the steps above.
Frequently Asked Questions: Sanitizing Your RV Fresh Water Tank
Most RV technicians recommend sanitizing your fresh water tank at least once a year, typically in spring when dewinterizing your RV. If your RV sits unused for 2–4 weeks or more, consider sanitizing it before each use to ensure the water is safe for drinking and cooking.
Use 1/4 cup of regular household bleach (5–6% sodium hypochlorite) for every 16 gallons your fresh water tank holds, or 1 ounce per 8 gallons. For a 50-gallon tank, that’s about 3/4 cup. Always dilute the bleach in at least one gallon of water before adding it to the tank.
Leave the bleach and water mixture in your fresh water tank for at least 12 hours but no more than 24 hours. Leaving it longer risks damage to rubber seals and gaskets in your water system.
Yes. If you prefer to avoid bleach, use a biodegradable, RV-approved fresh water tank sanitizer (these are available at all Camping World locations). Follow the same basic steps, but substitute the manufacturer-recommended amount of the sanitizer product for the bleach mixture in Step 3. Always verify the product is approved by your RV’s manufacturer.
Partially. When you run the bleach solution through your water lines and out of your faucets, it passes into the gray water tank. This can help reduce bacteria in the gray tank, but it’s not a substitute for dedicated gray tank cleaning. It’s also important not to let the bleach solution sit in your gray holding tank. Drain it promptly once the flush cycle is complete.
Vinegar is not an effective sanitizer for RV fresh water tanks. It does not reliably kill bacteria and pathogens the way properly diluted bleach or an RV-approved sanitizer does. White vinegar can be useful for removing mineral deposits or as a rinse aid to help neutralize bleach odor during Step 6, but it should not be used as a substitute for a full sanitization cycle.
If your RV’s fresh water inlet has an overfill vent that blocks a funnel, pour your diluted bleach solution directly into your fresh water hose before connecting it to your water source. Hold the unconnected end of the hose higher than the connected end, then attach the hose to a water spigot and turn it on. The water pressure pushes the bleach solution through the hose and into the tank, and, as a bonus, it sanitizes the hose.
To drain your RV fresh water tank, locate the tank drain valve and low-point drain on the underside of your coach (often color-coded red for hot water and blue for cold water — check your owner’s manual if you’re unsure). Open the low-point drain valve and allow gravity to pull the water out. Opening all your interior faucets while draining helps air enter the lines and speeds up the process, similar to lifting your finger off the top of a straw.
Fresh water isn’t something to take for granted when RVing. Luckily, this sanitization process is easy, and you only need to do it once a year to continue enjoying the benefits of RV living. Here are some additional maintenance resources:
What’s been your experience sanitizing your RV’s fresh water system? Leave a comment below!
