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The Complete Newbie's Guide to an RV Water System

The Complete Newbie's Guide to an RV Water System

Water is one of the main benefits that make camping in an RV so convenient—you've got fresh water, showers, and indoor plumbing right there at your fingertips. No going to bed covered in sweat and bug spray. No finding a private tree in the middle of the night. Just turn the faucet and boom—it's like magic. But if you're brand new to RVing, it helps to understand how the magic works. What is fresh water, gray water, and black water? How do you actually get water in your RV? We'll pull back the curtain in this article and show you how it all happens. It's actually pretty straightforward once you know what you're looking at. Let's get started. In this article:

How an RV Water System Works

You'll hear three common terms when discussing RV plumbing: fresh water, gray water, and black water. Fresh water is the water that goes into your camper. The waste water that comes out is called gray and black water. Gray water is the waste water from your sinks and shower. Black water is the waste from your toilet. (If you've ever seen National Lampoon's Christmas Vacation, black water is what cousin Eddie was emptying in that iconic "sh*##er's full" scene. If you haven't seen this 1989 classic, I recommend it for your next movie night.)There are other components to your system, like pressure regulators and water pumps and heaters, but at its core, this is how an RV water system works: fresh water in, gray/black water out. So—how do you get the fresh water into the RV? You either use your city water connection, or you fill your fresh water tank. If you use a city water connection, you'll have built-in water pressure and won't need your pump running. If you fill your fresh water tank, you'll need to turn your water pump on to push the water from the tank to the rest of your RV (more on this below). Note: Don't just go sticking any hose into your fresh water tank. Purchase a hose specifically for potable water (these hoses are usually white or blue), and only use it for this purpose. Never, ever mix up your drinking hose with your sewer hoses...for obvious reasons.
Diagram - Fresh water flowing into black and gray tanks in an RV
RV Fresh Water and City Water Connection
RV Fresh Water and City Water Connection
RV Water System Diagram

Method 1: How to Connect RV to City Water

City water just refers to the water hookup you'll find at many campgrounds. When you book your site, you'll pay to use the water hookup and have access to unlimited water during your stay. To hook up your city water connection, just take your fresh water hose, attach it to your city water port (it should be labeled as such) and turn on the water. No need to use your water pump—the water from these connections is pressurized, so all you have do is turn it on, just like you would at home. This water will then flow throughout your camper and provide the H20 for showering, cooking, flushing the toilet, and washing up. I also highly recommend always using a water pressure regulator any time you use a city water connection. These are inexpensive safeguards that protect your RV's plumbing system from potentially damaging water pressure. The ideal water pressure for most RVs is somewhere between 40 and 60 psi, but not all campgrounds stay within this pressure range. These regulators are so useful that they're typically one of the first products recommended to new RVers off the bat.
Watch now: hooking up a city water connection at a campground

Method 2: How to Fill Your RV Fresh Water Tank

If you won't have access to a city water connection (such as when you're boondocking, ie camping without hookups) you'll fill up your RV's fresh water tank before you get to your campsite. Your fresh water tank can only hold so much (usually anywhere between 20 and 100 gallons, depending on its size), so once it's gone, you'll need to refill it. You can bring an extra, portable water tank to make your trip last longer. It's also a good idea to get comfortable conserving water (check out some tips on that here). To fill your tank, take your fresh water hose and slide it into your tank inlet (it should be labeled on the side of your RV). Your fresh water sensor should let you know when the tank is full (or if the water comes bubbling up out of the tank, you know it's full). For an easier time filling the tank, I recommend picking up a tank filler for a few dollars. This will help prevent the hose from falling out of the tank during filling from the water pressure forcing the hose backward.
Man feeding fresh water hose into fresh tank fill on RV
Fresh water connection with hose attached on RV

Using Your RV Water Pump

Because there's no pressure behind the water just chilling out in your fresh water tank, you will need to turn your pump on to use this water. In fact, it's usually okay to fill your tank, turn your pump on at the campsite, and leave it on until you get ready to leave. The pump works on demand, so it should only operate when a faucet is open or a toilet is being flushed; thus the power draw is extremely minimal. The only constant power draw from the pump is really the little indicator light showing that it's on. Many people prefer to leave the pump on for the duration of their stay. That said, I'd recommend turning your pump off while you're driving or if you're leaving your campsite for an extended period of time. This is more a "just in case" provision than anything. It's not unheard of for a faucet to shake itself on during a bumpy drive or for a leak to occur in an RV that's been left unattended. If this happens, you'll definitely want your water pump to be shut off. You'll also want to turn the pump off if you switch to city water. Otherwise your pump will continue to draw from your fresh water tank when you'd probably rather save that water for later.
Water Plump Control Panel Switch on RV

Where to Refill Your RV Fresh Water Tank

So where do you get this water to fill up your tank? Many campgrounds, dump stations, rest stops, gas stations, RV parks, travel centers, and other parks have water fill stations for your to use. Some charge a fee, while others are free. Some stores, like Walmart (friend to RVers everywhere), often even have a water fill machine. The main thing to remember here is to always use potable water. Look for signs that indicate potable water, which means the water is safe to drink.
Potable vs non-potable water signs
Water Pump Gas and Electric Control Switches
Water heater bypass switch on tankless heatear
Bypassed vs non-bypassed water heater graphic

How to Use an RV Water Heater

Like hot showers? Me too. To enjoy those, you'll need to turn on your RV's water heater at the start of your trip once you get to the campsite. Using your RV water heater is pretty straightforward. The key thing to remember is to only turn your hot water on AFTER your hot water tank is full of water. Otherwise, you risk burning it up, since water heaters aren't designed to run without water inside the tank. (Note: this only applies to standard water heaters, not tankless water heaters).

How to Fill Your Hot Water Heater

So how do you fill your hot water tank, and how do you know when it's full? Hot water faucets get their water from your heater, so if water comes out of the hot faucets, it means the heater is full. Go ahead and open a hot water tap in your coach. This will flush any air out of the lines and let the water come through. Once you see water, you know the tank is full, so you can go ahead and turn the water heater on using the control panel in your coach. (You'll only need to fill the tank at the start of your trip, then you should be good to go.) Pro tip: Make sure your water heater bypass valve is closed when filling up your system with water. The bypass valve is designed to direct flow away from the heater for winterization purposes, so that you don't fill up the hot water heater with antifreeze. However, you want to close the valve during the camping season so that water can enter the hot water tank. (Read more about winterizing your camper here.)Just like your water pump, you can leave your water heater on while you're camping. Many campers choose to leave their water heaters on while hooked up to campground electric but turn them off between uses when running on propane to save fuel. And because a lot of people are worried about burning up their heater if their fresh tank runs out of water (such as while boondocking), I want to assure you that you'll be aware of the empty fresh tank well before your hot water tank runs dry. Your water pump pushes water from the fresh tank into the water heater. So when the fresh water tank runs dry and the pump has nothing left to push through, there will still be leftover water in the hot water tank at the point your water pressure calls it quits. Converting to a Tankless Hot Water HeaterTankless water heaters are becoming more common, and it's easy to see why they're such a hot commodity in the RV world. Unlike standard tanks that run out of hot water quite quickly (most heaters only hold about 4 - 10 gallons of hot water), tankless water heater don't have this limitation. Instead, tankless heaters warm up your water instantaneously when you turn on a hot water faucet. As long as you have a water supply, you'll have as much hot water as you need. Tankless water heaters tend to be more expensive, but they can be well worth the upfront cost if you find yourself consistently running out of hot water when you camp.

How to Drain an RV Fresh Water Tank

If you filled your fresh water tank and have water leftover from your trip, or if you're ready to winterize your camper and there's water in the tank still, you'll need to drain the water tank. Fortunately, this is pretty easy to do. Just locate the low point valve(s) beneath your RV, uncap it, and let the water drain out. This should leave your lines sufficiently drained between camping trips. However, if you're winterizing your camper, you'll need to take a few extra steps to make sure there's no water leftover in the camper. Note: Do NOT confuse your low point valves with your black and gray tank valves. If you do, you'll a) immediately regret it and b) have a hell of a story to tell. Pictured below: examples of low point drain valves on RV. They may look a little different depending on your rig.
RV Low Point Drain Valves
Fresh Water Valve with Water Draining

How to Sanitize and Clean an RV Fresh Water Tank

This is the water you're using to drink, cook, and shower with, so you want to make sure the tank it comes out isn't growing some kind of moldy, bacteria-ridden science project inside. You should aim to sanitize your tank at least every 6 months, but you can certainly do it sooner if you notice an issue, such as a bad smell or discolored water. These are major signs that something is wrong in the tank. Even if you don't plan on drinking the water, if you use your fresh water tank at all (for showering, washing dishes, etc.), it's important to make sure your tank is clean and bacteria-free.
  • Drain your system. This means the fresh water tank as well as your water heater. Use your low point valves to drain the fresh water tank. There should be a drain plug on the outside of your water heater as well. Once everything is well drained, plug it all back up for step 2.
    Low Point Drain Valves
    Water Heater Drain Plug
  • Add some bleach. Use 1/4 cup of bleach for every 16 gallons your fresh water tank holds. So, if you have a 40-gallon water tank, you'll need 5/8 cup of bleach. Dilute it with around a gallon of water (never pour straight bleach directly into your tank), then pour the mixture in.
    1/4 Cup Bleach for every 16 gallons in fresh water tank + 1 gallon of water
  • Fill your tank completely. Make sure to use potable water. You want the bleach and water mixture to fill the entire tank and sanitize every inch of it.
    Filling RV Fresh Tank
  • Turn on your water pump and faucets. Turn each faucet on (cold AND hot sides) until you smell bleach coming out of it, then turn it off and move to the next faucet. Make sure to get your shower too!
    RV Sink
  • Wait 12-24 hours. Let that soak in your water lines and tank and kill any bacteria that might be residing there.
    Fresh and City Water Inlets on RV
  • Empty out the cleaning mixture. Drain your tank using your low point valve(s), then fill up the tank again with a new round of fresh water. Go through your RV and open up each faucet, letting water run through them until you no longer smell bleach. (Although if there's a tiny bit of bleach residue leftover, it won't hurt you in this diluted state.)
    Low Point Valves
    RV Sink
Keep in mind that, although sanitizing the tank should leave it perfectly safe to drink from, you're not required to use your tank if you aren't comfortable with it. If you're really concerned about drinking water from a tank you can't see inside of, you can always just use bottled water during your trips and avoid the issue completely. I personally know several campers that do this. If you're renting your RV or you purchased a used one and you're not sure about the state of the tank interior, it's perfectly fine to rely on the tank as much or little as you're comfortable with.

How (And Where) to Dump Black and Gray Water

Remember that lovely topic we talked about earlier—black and gray water? Well, they're kind of the price you pay for having sinks and a shower and toilet onboard. Eventually the time will come when you have to (gasp) dump your waste water. This is usually the part every new RVer dreads doing for the first time, but I promise—once you do it a few times, you won't think twice about it.The most common dumping location is at an RV campground. Some places have a dump station right at your individual site; others have a designated station for all RVers to share. If you're not at a campground, you can usually also find dump stations at truck stops, RV dealerships, gas stations, or even some sewer treatment plants. (Note that some of these are free, though others charge a small fee.)To drain your waste tanks:
  • Take your sewer hose, open the sewer connection cap, and firmly attach the hose. I recommend picking up a clear hose fitting for the connection between your hose and waste valve on your RV. You may not want to see what comes out, but it'll be easier to know when your tank is finished emptying this way. NOTE: MAKE SURE YOUR SEWER VALVES ARE CLOSED BEFORE YOU REMOVE YOUR CAP. Otherwise the, ahem, material, will come flooding out. Then, attach your sewer hose, making sure it's nice and secure.
    RV Sewer Hose Cap and Valves
    Remove your cap
    Sewer Hose Attached to RV Waste Station
    Attach your sewer hose
    Clear Sewer Hose Fitting
    You can also use a clear sewer hose attachment here to see when your tank runs clear
  • Attach the other end of the hose to the dump station. I highly recommend picking up a sewer elbow if you don't already have one, preferably a clear one. These make it much easier to connect to the dump station and tell when your tanks are finished draining so you don't pull the hose out before the job's done. This can get disastrous pretty quickly. The friend I mentioned earlier, Jake, had just this experience on a camping trip before he bought his elbow adapter. He thought his tank was finished draining, pulled out the hose, and found his gloves immediately filled with...well, you can guess. (You can get Jake's tips and hear him tell that story himself here.)
    Clear Sewer Elbow Attached to Hose at RV Dump Station
    Dump Hose Draining Waste Tanks on RV
  • When you're ready to dump, open your black tank valve first and let the tank empty completely, then rinse out the tank with a flush valve to clear out any remaining gunk and give your sensors a spray down. Next, open your gray tank and let that drain (the gray water will help wash the black water residue out of the hose). Shut the valves again, disconnect your sewer hose, place the sewer cap back on, and you've officially survived dumping your waste tanks.
    Pulling Black and Gray Waste Tank Valves
If you need a little more detail on best dumping practices, we get into the nitty gritty intricacies of dumping your black and gray tanks here.
Now that you know how to get fresh water into your camper and take care of your water system, you're just about ready to go anywhere. Here are a few other resources on RV plumbing to help you out: Still have questions? Let us know in the comments below!
Amber S.
About Amber S.As a content writer for etrailer, I might spend my morning loading and unloading a bike on five different bike racks to figure out which is easiest to use. I might be in the parking lot, taking pictures of an impressive RV battery setup our techs came across in the shop and discussing the benefits of the setup with the owner. I might spend an afternoon in a manufacturer training classes for some hands-on experience with new products, and then sit down to assemble all this information into a coherent article.At etrailer, one of our core values is that we are always learning, and I learn something new every day. I start each morning with the goal in mind of taking all of this information and figuring out the best way to answer the questions people ask us (and the ones they don’t know to ask yet), and helping people get the solutions they need to make their lives easier, safer, and more fun. I’m a DIYer at heart, so it brings me great joy to help a fellow DIYer find what they’re looking for, whether that’s a product, an answer, or a community.
Related ArticlesRelated ProductsWritten by: Amber S.Updated: 10/9/21


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