How Big Are RV Water Tanks?

An Explanation of Water Tank Capacity

An RV has the ability to carry an average of 20-100 gallons of fresh water into the backcountry, allowing you comfort and peace of mind as you enjoy your escape into nature.

The popularity of adventuring in motorhomes and RVs is largely due to their ability to bring the modern comforts of your home, into the outdoors. And what is everyone’s favorite modern amenity? Indoor plumbing. And if that’s not the first thing that comes to your mind, it should be.

how big are rv water tanks

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Seriously, just spend a couple of weeks backpacking in the mountains or even in some foreign countries, and you’ll quickly develop a stronger appreciation for freshwater on-demand.

While camping, most people are going to interact with their RV’s plumbing system throughout the day, every day. Think about it. Between cooking, cleaning, and using the bathroom, the plumbing in an RV lies at the core of many daily chores.

Because of this, it is crucial to know the ins and outs of your own plumbing system and to be an informed buyer when looking to purchase an RV.

Read on to learn what to look for when inspecting an RV’s water tank situation and how to care for your own RV plumbing system so that you can avoid a really nasty mess.

RV Holding Tanks

Most RVs have three separate water holding tanks. These tanks are all part of your camper’s plumbing system and play very different roles in supporting that system. Each tank will need specific, specialized care in order to maintain proper functionality. I have already covered an article on the working of an RV holding tank sensors.

The three types of water holding tanks you’ll utilize in your RV are the fresh water tank, grey water tank, and black water tank.

Freshwater Tank

RV freshwater tank

Your freshwater tank, as the name implies, holds your fresh, potable water. Potable is a term that refers to whether or not water is safe for human consumption. You’ll see that term as a label on spigots at RV campgrounds, gas stations, or anywhere that has a freshwater connection.

If a spigot is labeled non-potable, do not fill your freshwater tank with it. Non-potable water has not been filtered or processed and should not be considered safe for human consumption.

Grey Water Tank

The grey water tank holds water that has been used and is now considered spoiled. Appliances that drain into your grey water tank will be the faucets in your bathroom and galley, and if your camper has one, your shower.

Generally, grey water is a byproduct of cleaning dishes, washing food, or bathing. It is called grey water because it often will have a greyish hue to it when drained from the tank.

Black Water Tank

The black water tank is often referred to as the “septic tank” or “waste tank”. This tank holds liquid and solid waste that drains from the toilet in your RV. Only RVs with toilets have a black water tank.

Occasionally you may come across a camper that has a combination of grey and black water tank. These tanks hold all the dirty water that drains from your RV.

These tanks are called “black water” because when drained, the water is significantly darker than the grey water tank.

Holding Tank Capacity

Arguably the most important detail to know about your RV’s holding tanks is their capacity. Some regions even require the capacity of water holding tanks to be documented when registering the vehicle.

An RV often comes with a three-number label that refers to the capacity of the holding tanks. This number can be written in X-X-X format. So, for example, if you see a label saying 50-35-30, that means the fresh water tank capacity is 50 gallons, the grey water tank holds 35 gallons, and the black water tank holds 30.

You won’t always find the tank capacities labeled this way, but you’ll always be able to locate capacities somewhere on the RV or in the user manual.

Typical Capacities

Average holding tank sizes are tricky to pin down, as they can vary significantly from each manufacturer.

Typically though, you can expect an RV’s fresh water tank to hold anywhere from 20-100 gallons of water. A large Class-A RV rarely comes with a freshwater tank smaller than 60 gallons. Class-C RVs hold anywhere from 35-60 gallons while a class-B RV and campers like this adventure camper range from 20-40 gallons.

Note: Don’t be confused by the letters associated with RV sizes. From largest to smallest, it goes class-A, class-C, class-B+, class-B. Weird, I know.

What Size Tanks Do You Need?

So, how big are RV water tanks? A common size of RV freshwater tank is 40 gallons, and so people often inquire as to how long a 40-gallon tank will last them. This will vary wildly from person to person, as will require holding tank capacities. Here are some factors that will play into the size of tanks needed:

  • How much water is used for cleaning and bathing
  • Amount of people camping/living out of the RV
  • How many days were spent boondocking vs days spent in a campground with a water hookup
  • How much water is consumed for hydration
  • Amount of water used for cooking

Spend some time thinking critically about these factors. It is crucial to have the proper RV holding tank size so you don’t have to make cumbersome trips into town to dump stations, and so that you never run out of fresh water for drinking. Running out of fresh water is scary and can be life-threatening. Please never drive into the remote wilderness without ensuring you have an abundance of fresh water.

Importance of Fresh Water While Camping

fresh water

When I was around 20 years old, I took my first solo road trip around the west half of the United States. While gearing up for this epic adventure (it was seriously so epic), I picked myself up two 5-gallon water jugs. These jugs were super tough, BPA-free, and most importantly, held more than enough water for my daily needs and an emergency reserve.

With that said, 10 gallons is not a ton of water. I wanted bigger containers, but I was limited by space in my truck and ended up having to refill every week which was a hassle. Even so, when those puppies were full, I knew I could confidently drive into the desert by myself and have plenty of water to thrive.

RV Life

When adventuring in your camper, you’ll need enough fresh water to perform all daily chores and keep yourself hydrated while also having an emergency reserve. Because of this, you’ll want to pay particular attention to the size of your freshwater holding tank and determine if it will meet all your demands.

Tips on Filling Your Freshwater Tank

Use these tips to make filling your fresh water tank a seamless, safe, and hassle-free task.

Potable Water Hose

Buy and utilize a potable water hose. A potable water hose is a hose you will use solely for the purpose of filling your fresh water tank. They are typically white in color and are made of a material that doesn’t leave a synthetic taste in the water.

Use Safe Spigots

Dry Water Null

Only fill using spigots that are labeled “potable” or “drinkable”. Even if it takes a long time to find a spigot offering drinkable water, never compromise and fill with unknown water. This is especially pertinent if you are traveling in a country that has questionable city tap water.

Use Separate Hoses

Never use the black water drain hose for filling your fresh water tank. Doing this could be exceptionally harmful to your health and would quite frankly be really gross.

While I think this would be difficult to do in the first place because the hoses are very different sizes, I think it is still worth saying. Be safe with drinking water.

Water Treatment Tablets

Similar to what backpackers use to purify water in the backcountry, some companies offer water treatment tablets that you can put into your freshwater tank to help purify the water and prevent the growth of bacteria in your tank. The best tablets for this process are made with chlorine dioxide, a chemical that is safe for human consumption in small concentrations.

If you choose to use treatment tablets in your tanks, please do extensive research on the tablet you choose, and be careful with how much you use.

How to Measure Water Holding Tank Capacity

Sometimes, for whatever reason, it is difficult to pin down the exact capacity of your camper’s holding tanks by inspecting the RV. If you find yourself in this position, there are ways to measure how many gallons each of your tanks hold.

Internet Research

The first route you should take is to simply hop on the internet and look up your RV’s make and model. You should be able to find the dimensions and capacity of your holding tanks on the manufacturer’s website.

Calculating Yourself

If internet research yields no results, you’ll have to try a slightly more engaged process. Find where each tank lives in your camper and using a tape measure, measure the height, width, and length of each tank. Use those values to find the total volume in cubic feet or inches (or centimeters if you roll like that).

Then hop back online and use a converting software to convert the cubic volume into total gallons. Boom, there’s your holding capacity.

If you don’t have physical access to your RV holding tanks and absolutely need to know the dimensions, you can pay an RV technician to do this process for you. A technician will have the tools and know how to safely access the tanks and grab dimensions for you.

Draining Waste Tanks

The not-so-glamorous side of owning and traveling in a camper. This chore is not even remotely fun, but with practice can be a quick, simple process.

Black Tank

After finding a dumping station, position your RV’s drain valve near the dumping port. Connect your wastewater hose to your RV and to the dumping port and open your black tank’s valve. You should hear or potentially even see your black tank draining into the dump station’s tank.

Grey Tank

You should try to always drain your grey water tank after draining the septic tank. This is for the simple purpose of allowing the flow of grey water to clean out human waste from inside your hose after draining the black water tank. The process follows essentially the same steps as draining the black tank.

Free Flowing Grey Water

While boondocking, some people choose to leave their grey water tank open and let it drain onto the ground as they produce it. This can be done safely without hurting the environment by using biodegradable soaps for every single cleaning process.

This means you need to use a biodegradable soap for washing hands, dishes, body, hair, and everything. If you choose not to use biodegradable soap, you will be releasing synthetic chemicals into the environment and hurting the natural habitat for flora and fauna. Please don’t do this.

I suggest playing it safe and waiting to dump at a real dump station.

Conserving Water

Practice conserving water to reduce the frequency at which you have to refill your fresh water, and dump your wastewater.

Military Style Shower

The average American shower is 8 minutes long and uses just over 17 gallons of water. If you use this much water every time you use your RV shower, you’ll have to constantly be refilling your fresh tank, a tedious and time-consuming task.

Follow these steps to take a water-conserving style shower often referred to as a military-style shower:

  1. Remove clothes and step into the shower before turning on the water
  2. Turn on the water and quickly wet your entire body and hair, turning it off once fully wet
  3. Lather your body with soap and your hair with shampoo
  4. Turn the water back on and rinse quickly and effectively
  5. Turn off the water as soon as all soap is rinsed

This may not be the warmest or most pleasant shower you’ll ever take, but it will save you a heck of a lot of water.

Efficient Dishwashing

RV Dishwashing

Washing dishes is another task that typically consumes a lot of fresh water. Try adopting the military style shower technique for washing dishes in order to preserve your fresh water.

Pro-tip: Dr. Bronner’s is a great, all-natural castile soap that smells great and is biodegradable. They are not affiliated with this blog in any way; I just seriously love their soap. Check ’em out.


Please don’t conserve water by not hydrating properly. Hydrating is so important to health, and you can end up in dangerous situations if you are not drinking enough water every day.

This is particularly true in deserts; a popular boondocking environment amongst RVers.


Winterizing refers to the process of preparing your RV for less or no use over the winter months. This is a vital process to do every autumn if you wish to protect the investment in your camper. Without proper winterization, you run the risk of damaging most, if not all of your plumbing system as water expands while freezing.

This expansion can cause pipes to burst which then can result in mold or rot damage if an unnoticed, burst-pipe leaks into your walls, floors, and cabinets. Freezing water can also crack components in your water pump, water heater, and faucets, leading to costly repairs.

The people over at Fraserway RV wrote a great article detailing how to fully winterize your RV. Give it a read to learn what steps to take to winterize your own plumbing system.


If you are looking to buy an RV, use your newly learned information to make an informed decision before you purchase. If you already own a camper, I hope this article has helped you to learn a bit more about your holding tank system and how to care for it.

Happy camping!

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About Author

Schuyler has been working and playing outdoors his entire adult life. As a ski-bum in his early 20’s, he began building campers in the beds of pickup trucks to pursue a life of freedom and adventure. After a decade of experience as an artist and carpenter in Washington State, he moved to Colorado to work as an RV technician, converting vans into luxury campers. Now he is traveling the world, using writing as a way to continue his passion for creativity and artistry.

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