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RV Water Flow Meter: Know How Much Water You Use!

RV Water Flow Meter: Know How Much Water You Use!

When we’re boondocking (our absolute favorite way to camp!), we need to keep an eye on our water usage. Anyone who boondocks, especially for long periods, understands the importance of water conservation to extend that trip for as long as possible. Knowing exactly how much water you have to work with is good information. There are other reasons to monitor water flow as well. For example, we read about a guy who was flushing his black tank and inadvertently caused an overflow up through the toilet causing quite a mess in his RV. So, today we’re looking at an effortless way to monitor the amount of water going into (or out of!) your fresh water tank, (or even going into your tank flush!), by using an RV water flow meter.

Let’s dive right in!

What Is an RV Water Flow Meter?

An RV water flow meter is a small device that attaches to your hose and then gives you a digital read-out of the number of gallons flowing into your fresh water tank – or elsewhere.

These are generally small, lightweight devices, made of plastic, and not too expensive, though there are fancier water flow meters for other purposes.

But for the purpose of today’s post, measuring water flow for use with your RV, we’re talking about small RV water flow meters that weigh just a few ounces.

Where and How Do I Install an RV Water Flow Meter?

In the simplest application, an RV water flow meter just screws right in line with your hose. You screw one end of the water flow meter onto your water hose, and it will measure the amount of water flowing out of the hose, through the meter (and into your fresh water tank or wherever you’re using it), and give you a digital read-out of that measurement.

A meter installed inline with a water hose

An RV water flow meter connects to your water source and to your water hose to measure the flow of water entering your tank, or in line to the water outlet of your plumbing to measure the flow of water out of the tank. (Photo credit: P3 International via Amazon)

An advanced option for installing an RV water flow meter would be to plumb a meter into the internal plumbing of the RV where it could track the amount of water flowing OUT of the fresh water tank, thus giving you a reading of the amount of water you’re using while you’re camping.

This would require some minor DIY plumbing skills, but it could be done fairly easily, and we’re sure that someone, somewhere, has done it to keep an eye on the amount of fresh water being used, especially because RV tank monitors can be especially unreliable.

For information on how to keep your RV tank monitors working more reliably, see our post, “4 Ways to Clean Your Tank Sensors”.

Why Would I Want an RV Water Flow Meter?

Well, as we’ve noted, measuring the exact amount of water going INTO or OUT OF your fresh water tank are two good reasons to own an RV water flow meter.

The ability to measure the amount of water being used for your tank flush system, so you don’t overflow the black tank and/or blow the upper seal (which also happened in the case we mentioned in the intro), is another good reason why an RV water flow meter could be beneficial.

Particularly if you’ve got an older RV and your tanks are old, there can be struvite built up inside the tanks preventing your RV’s tank sensors from properly reporting tank levels. So using your tank sensors to monitor how much water your tank flush system has put in COULD end poorly.

If you’re not familiar with struvite, have a look at this:

And finally, an RV water flow meter installed in your plumbing system could allow you to measure how much fresh water you’re using when you’re boondocking, providing a more accurate reading than your holding tank sensors.

What Are Some Popular Options?

Three of the most popular RV water flow meters on Amazon are as follows. Bear in mind that these products use plastic components… so while they’re relatively inexpensive, you may also need to plan on replacing them now and again as the years go by. Let’s take a look…

Rainwave RW-9FM LCD Digital Water Flow Meter

This little water flow meter has a digital read-out and can be changed from gallons to liters if desired. It weighs under 3 ounces and is less than 9 inches long and a little over 4 inches wide. There’s a nice auto-off feature that turns off the display after a certain period of no use, saving your battery even if you forget to turn the device off.

On the plus side, reviewers note that this Rainwave digital water flow meter comes with the battery pre-installed, and is waterproof to protect the electronics. One reviewer notes that he doesn’t like to travel with a full 50-gallon fresh water tank because it impacts his fuel consumption. So, he uses his water flow meter to put 20 gallons into the tank before leaving on a trip. The device allows him to know exactly how much water he’s putting into his tank.

On the downside, some reviewers who left the device on their hose permanently noted that weather impacted the screen and made the digital display foggy over time. Some reviewers note leaking as well. (There’s a small rubber washer which we suspect based on other reviews could be related to leaking issues… which is easy to replace.)

Rainwave RW-9FM Digital Water Meter - Accurate Water Usage Measurement - Helps Conserve Water and Costs
  • PERFECT FOR MEASURING: Measure how much water it takes to fill up your pool or water the plants in your garden. GREAT FOR RVs.
  • DIGITAL DISPLAY: Easy-to-read LCD screen displays your water usage in gallons or liters.

P3 Save A Drop Water Flow Meter

The P3 Save A Drop water flow meter is very similar to the Rainwave meter in appearance and function, though it’s a bit smaller… weighing in at under 2 ounces (which is about an ounce less than the Rainwave). It’s also about half as long at a little over 4 inches by 3 inches.

Its LCD digital display is noted as easy to read, however, this unit does NOT have an automatic shut-off which is a feature we found nice about the Rainwave product.

The P3 Save A Drop does get good reviews. One very impressed reviewer notes that his holding tank sensors are notoriously inaccurate and he appreciates the water flow meter for use with his RV so that he knows exactly how much water he’s carrying. Noting that every gallon of water weighs 8.34 pounds, he calculates how much weight he’s carrying when he travels with the help of this water flow meter.

Reviewers with negative experiences largely note an inaccuracy in flow reporting or that the display stopped working.

We’ll note here that these plastic water flow meters are not designed to sustain exposure to temperature extremes. So, leaving one on your water hose through a hot summer or cold winter may well result in a cracked, leaking, or non-working device.

Save a Drop P3 Blue Water Flow Meter | Measure Gallon Usage from an Outdoor Garden Hose | Helps Conserve Water……
  • Use the easy to read meter to measure how much water is flowing out of the hose
  • it calculates both accumulative watering volume and singular waterings

Orbit Hose-End Water Flow Meter

At 3.25 inches long, this Orbit device is the smallest of the three water flow meters featured here. It weighs just under 2 ½ ounces and is the least expensive of the three meters we’re featuring, but in tandem with its price are the most negative reviews of the product.

Positive reviews note the accuracy of the measurements, and negative reviews largely center around leaking or breakage, the face of the digital display wearing off, and a lack of durability.

Orbit 56854 Hose End Water Flow Meter
  • WATER CONSERVATION: Measure water consumption to prevent over watering.
  • KNOW THE FLOW: Calculates both single-use and total water consumption.

How Accurate Are Hose-End Water Flow Meters?

Checking the Amazon reviews there are many reviews extolling their accuracy and others stating that they’re highly inaccurate. If you take a balanced view of the reviews, though, they appear to be fairly accurate. One reviewer noted that despite minor inaccuracies, he has found his RV water flow meter to be far and away more accurate than his tank sensors!

We also want to note that each of these little meters offers a read-out not only of the current measurable amount of water flow but also of the total amount over time (until you reset it).

What’s the Best Way to Monitor How Much Water Remains In My Fresh Water Tank?

There are a few ways to monitor how much water remains in your fresh water tank. One way is to keep your tank sensors clean and working well. This requires a bit of attention to regular maintenance.

You could also consider upgrading to a more accurate tank level monitoring system like the SeeLevel Tank Monitors.

And finally, you could consider doing as we mentioned earlier in the article and installing an RV water flow meter in line with the outlet line from your fresh water tank as a means of monitoring how much water you’ve used. You could even use two water flow meters in this case – one at the hose measuring the amount of water going in, and one in line with your fresh tank’s outlet line to measure the amount being used.

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Saturday 27th of May 2023

I would like a 1/2" small mechanical flow meter that could go between the pump outlet and outlet line

John Koenig

Sunday 27th of February 2022

I had bought an inexpensive water flow meter (about $20) on Amazon several years ago. It worked GREAT the first five times I used it (as a Full Timer, I filled my fresh water tank once a week and, each week, the meter showed 85 gallons). The SIXTH time I went to use it, it "popped apart" and would NOT snap back together and stay connected. MANY Amazon purchasers reported having a similar experience. How many times have you used the "Rainwave RW-9FM LCD Digital Water Flow Meter" and, when did you buy it?


Monday 28th of February 2022

Hi John. Sorry to hear your flow meter lasted such a short time. Like most people, we often rely on reviews and ratings to make purchase decisions. When we list multiple options in an article, we know that most gear has both pros and cons, and not everyone will have a great experience, even if reviews are pretty positive overall, like the flow meter you mentioned, which has a 4-star rating on Amazon. We don't buy, test and review each one, but try to be sure to highlight the most common comments, both pro and con, as we did here. When we have a specific choice that we've had exceptional experiences with, we'll always mention that, rather than listing popular choices and quoting from reviews. Sorry you had a poor experience with this.

Ed Fogle

Saturday 26th of February 2022

I use one of these meters when adding water before a trip. To not travel with the weight of a full 100 gallon water load I empty the potable water tank then use the gauge to add about 20 gallons. Plenty of water for two or three days of toilet flushing and hand washing.


Saturday 26th of February 2022

I think I've mentioned this before but if not, you can use your phone by just looking at the number of minutes (and/or seconds) as you fill your tanks and back flush them. Based on an average flow rate, test to see how long it takes to fill. You won't find the exact gallonage but close enough. If you're concerned about every six to eight pounds maybe you should try looking at your other cargo. If you have a trailer-try to place as much as you can toward the front if you think you have a marginal weight problem.

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