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The Dangers of Filling Your RV Water Tank Too Fast (or Slow)

When boondocking or camping in a dry camping spot, you must put water in your RV’s fresh water tank. However, what many RVers don’t realize is that the speed at which you fill up your fresh water tank matters. There are some dangers to filling an RV water tank too quickly or too slowly. 

To avoid any possible dangers with your RV, keep reading to find out how to best fill your RV water tank Let’s get started!

How To Fill The Fresh Water Tank On Your RV | Teach Me RV!

What Is an RV Water Tank?

An RV water tank is a tank the factory installs in an RV for potable water storage. Storing water allows RVers to fill up at a potable water source and haul the water to their campsite. This is convenient when dry camping, boondocking, or camping at a campsite without a water connection.

The size of an RV water tank typically varies by the type of RV. Smaller Class B conversion vans could have a water tank as small as 10 or 15 gallons. However, the lengthiest fifth wheels and Class A motorhomes can store 100+ gallons of potable water. 

Man refilling water tank
Filling up your water tank too quickly can cause some problems to your RV’s water system.

Where Do You Fill Water Tank in RV?

Where you’ll be filling your water tank will depend on the type of RV. Many models utilize the city water connection and require the RVer to make a few adjustments to knobs connecting to the plumbing system.

However, other RVs will utilize a gravity-based system similar to filling a vehicle with gas. Unlike the gas pump, you won’t have to panic when water starts shooting out of the water-fill port.

Finding a place to fill your RV water tank is typically very simple if you spend most of your time in a campground. If the campground doesn’t have water available at campsites, they’ll often have a water fill station at the entrance. Campers must stop here to fill up fresh, clean water before heading to their camp. If you’re boondocking, you can use resources like Campendium and iOverlander to scout nearby potable water sources.

RV attached to hose while refilling water tank
Be careful not to overfill your water tank when filling up.

Can You Overfill Fresh Water Tank?

Yes and No, most RV tanks are fine to be filled all the way. However, some might encounter an issue if filled too much.

Most RVs come with an overflow drain that leaks water when your tank is full. Once you notice the water pouring from the overflow drain, you should shut off the water flowing into your tank. If there is no overfill and the tank is gravity filled, it might overflow out of the fill spout.

The problem some RV’s have is that they can create a siphoning effect that drains some of the water out the drain hole when making a turn. Since its usually not possible not to make turns, some tanks benefit from not being filled all the way. Or if you encounter this problem, you can use some of the water by running a sink or flushing the toilet using the water pump. This helps prevent the overflow drain from creating a suction siphoning the water out of your fresh water tank.

Some RVers have arrived at their campsite to discover that the full tank is now half or three-quarters of the way filled because of the siphoning. You want to ensure the water stops flowing shortly after you stop filling the RV fresh water tank.

Pro Tip: Upgrade your RV water pump with one of these 5 Best 12V RV Water Pumps to make filling your RV water tank easier.

What Can Happen If You Fill Your RV Water Tank Too Fast?

While a fresh water tank will have an overflow, it can only do so much. If the water source pumps water into your fresh water tank faster than the overflow can expel the excess, it can pressurize the tank. If the overflow cannot keep up, the excess water could cause severe damage. Damage can occur even if the tank is not full too, because of air pressure. As you fill water air needs to escape and usually exits through an air relief; however, this needs to keep up too. Many times the air relief is right next to the fill, and rapid filling water can block the air hole.

The longer the water continues to rapidly fill your tank, pressure can build up in the tank. This could cause leaks in the tank, and leaks are an RVers nightmare. They can cause mold and water damage throughout your rig. It can be costly and challenging to repair unless you catch it early.

Worst case scenario, your water tank can even explode! While it did not happen to us, we once saw someone who was filling a gravity-fill tank with such high-pressure water it expanded the tank so much that it broke the supports under the RV as it ballooned. By the time the owner realized it, the tank had cracked and started pouring water out.

This was not because the tank was overfilled, but because the water was going in so fast, the air could not get out. It was actually air pressure that caused the damage.

Couple hooking up RV to water system to refill water tank
When in doubt, fill your water tank slowly.

Is It Possible to Fill Your RV Water Tank Too Slow?

The only negative to filling your RV water tank too slowly is that it can take forever. A water source with an RV-safe pressure will likely pump approximately four gallons of water per minute. If you have an 80-gallon water tank, it will take about 20 minutes to fill it when it’s empty.

If you fill your RV water tank too slowly, you’ll spend more time waiting for your tank to start overflowing. The only harm will be that you’re wasting time you could spend doing something else.

Pro Tip: For hopeful #VanLife explorers, you’ll want to know Do Campervans Have Water Tanks?

How Do You Know When Your RV Water Tank Is Full?

Most RV water tanks will have an overflow drain. This drain will start to release water once the tank is at capacity. Some RVers refer to this as their RV “peeing” because it mimics the sounds and resembles a dog peeing. However, RVs utilizing a gravity-fill system will likely not have this drain.

Rigs with a gravity system will start to gush water out of the fill port. Depending on the season, this can either be refreshing or terrifying. The more experience filling your RV tank, the more you’ll know when it’s almost at capacity.

RV attached to water system to refill water tank
If you don’t have a hose to hook up your RV to a water source, use a gravity-fill system instead.

How Do I Fill My RV Tank Without a Hose?

Sometimes you need to fill up on water, but you don’t have a lengthy hose or a water source nearby. In these instances, gravity-fill systems are the easiest solution. All you need to do is fill a few water jugs with clean, potable water and dump them into the fresh water fill port. You can continue this process until you’ve filled the tank.

If you don’t have a gravity-based system, you’ll need to siphon water into your fresh water tank. Depending on your RV’s plumbing system, you will likely need to make some knob adjustments. You can place a siphon hose in the water jug and turn on the water pump.

This method will siphon the water from the portable water jug through your plumbing system and into your fresh water tank. It may take more time, but this can be a practical way to fill up your tanks without packing up camp and taking your rig to the water source.

Some RVers who frequently run out of water will purchase large water bladders or tanks that fit in the bed of their truck. They’ll use an external water pump to pump the water from the bladder or tank into their RV’s tank. This makes filling your RV water tank faster and more convenient.

Pro Tip: These 7 Best RV Water Bladders will help you store more clean water while on the road.

RV TIPS: Fresh Water Tank Filling When It Shouldn't Be?

Can You Travel With a Full Fresh Water Tank? 

Traveling with a full fresh water tank is a hot-button topic. Some manufacturers state that their rigs can withstand traveling with a full fresh water tank; others say it’s not a good idea. Because of this, we’ll tell you to check with your manufacturer. If they correctly installed the water tank, it should withstand the bumps and dips along the road.

However, keep in mind that a gallon of water weighs eight pounds. Depending on your RV water tank size, you could look at several hundred pounds of additional weight. This can cause sway, reduce fuel efficiency, and potentially put you over your RV’s cargo-carrying capacity. Make sure you know the weight of your RV and how much you can safely add to it. 

What kind of water tank system does your RV have? Would you risk driving with a full water tank? Share your thoughts in the comments!

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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Saturday 3rd of December 2022

We have a 2017 Nu-Camp Outback Teardrop made in Sugarcreek, Ohio by the Omish. Couldn't ask for a better built trailer in all respects including driving with water in the tank since we boondock a majority of the time


Saturday 3rd of December 2022

Wow! A gravity fill tank exploding from too much pressure? Because its a gravity fill type tank, it wasn't the water pressure of the fill hose that caused the failure, it was the weight of the full water tank on those cheap self tapping screws that hold the tank straps to the frame that probably failed. Some RV owners that know about the screw failures will replace each screw with a grade 5 or grade 8 nut and bolt "before" those screws fail.

Mortons on the Move

Wednesday 7th of December 2022

They had the hose stuck inside the fill port and I think the air vent may have been clogged too. I think it was air pressure that broke it. But yes we have seen them just fall out of the RV too.