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RV Grey Water vs Black Water: Here Is The One Simple Difference

Kelly Headshot

By Kelly Beasley

Grey water VS black water. In an RV, what are they and what's the difference?

By the way, when you start RVing, be prepared to learn lots of new words.

You'll even come across camper slang- words like 'stinky slinky': a nickname for an RV black water hose.

Waste Master hose connected to RV

So, what is greywater, and what is black water?

And should they be spelled as one word or two (greywater VS grey water)? Haha, nobody really knows.

What CAN be answered is what each wastewater term refers to. Seeing as you're here, you're wondering.

So let's get right to it.

What Is An Example of Greywater?

'Greywater,' or 'grey water,' OR 'gray water,' ORRRRR 'graywater' (sheesh!) refers to the wastewater that comes from the liquids that go down your bathroom sinks and other drains in an RV.

Similarly, outside of the RV world, grey water is also wastewater collected from:

  • Sink drains
  • Shower/bathtub drains
  • Dishwasher
  • Washing machine

Basically, it's any liquid you drain that doesn't go down your toilet.

In your RV, the grey water ends up in grey water tanks (surprised?).

The grey tank is underneath your RV. It holds wastewater until you can dump it in an appropriate dump station.

Greywater is generally not as bacteria-filled as blackwater is.

RV grey wastewater mainly contains detergents from bathing and from sinks. It contains no harmful chemicals, as long as you don't use any.

RVs at busy campground

I like big butts and I cannot lie (sorry)

Untreated greywater can be used (sans any harmful chemicals) for things like watering to nourish plants or even for flushing toilets.

You must be careful what kind of soaps you use. Otherwise, you might kill plants. (It's not a bad idea to catch this water for this type of use before it goes into your tank).

What Is Considered Black Water?

Black water is considered the wastewater that comes from everything flushed down your RV toilet.

Naturally, it will contain fecal matter, urine, and TP. It's also called sewage or brown water (but in the RV world, it's always referred to as black water).

Sewage contains a lot of disease-carrying bacteria and sometimes even a black tank treatment, if you use those.

Natural reasoning tells us that blackwater is much more dangerous to humans, left untreated.

Thankfully, we don't have to treat our own. Fecal contamination of wastewater is left up to the city treatment plant it's dumped into (AND LIKE THANK GOD, RIGHT???).

Sure, you must deal with your human waste more in an RV than you do in a house, but there's not much you have to do with it besides capture it in your camper black tank and then dump it.

What Is The Difference Between Blackwater and Greywater?

Grey water VS black water: The difference between blackwater and greywater boils down to the contents they contain.

Blackwater contains urine and human waste which is essentially sewage. Therefore, it has much more harmful bacteria and pathogens than gray wastewater does.

Greywater contains only dirt and food particles from washing dishes, showers, food scraps and it may have some detergents.

Why Have Holding Tanks At All?

You may wonder, if you always camp where you have access to connect to a dump, why RVs have holding tanks.

They have RV waste water tanks because sometimes campgrounds don't have full hookups. Meaning there may not be access to a dump at your campsite.

Also, many people like boondocking, which is almost 100% of the time dry camping.

Therefore, your recreational vehicle needs to contain your waste until you have dump access.

A couple sitting in chairs in front of Class A RV

Why Do We Separate Greywater And Blackwater?

Why we separate greywater and blackwater is a pretty good question when it comes to RVing. I'd never thought about it until now.

Honestly, the two types do not HAVE to be separated.They always get dumped into the same septic tank or septic system, so why separate them?

In fact, with some small RV trailers, the wastewater tanks are not separated.

In those cases, all wastewater flows into one tank instead of two or more.

When this is the case, it's automatically a black water tank because it contains black water sewage.

So why are they separated when you dump them both into the same place? Here are a couple of reasons it can be of benefit:

Dry Camping Benefits

One benefit to separating the two is when one is dry camping (camping without access to external utilities such as power, water, or a dump).


Dry Camping McCall Idaho

Because there are places (few, but there are some) where it is legal to dump your grey water on the ground if specific rules are followed.

Dumping grey (legally) at your site extends the length of your dry camping stay.

Just be careful you don't fill your black tank quickly and you can stay longer.

I shouldn't have to say this, but never, EVER dump your black tank on the ground, ANYWHERE.

There are ways to slow the filling of your black tank.

Let's look at a few ways:

  • Don't put toilet paper down your RV toilet (place into nearby trash)
  • Urinate outside as much as possible
  • Use the bathroom as much as you can when you are in town
  • Get a composting toilet

Rinsing Out Your Sewer Hose

One more possible reason for separating gray from black is to 'rinse' out your sewer hose. Here's what I mean.

If there is no water available at a dump you go to, there is no way to rinse out your sewer hose.

This is why you should always dump your black tank first, followed by the gray tank. The gray water 'cleans' out the hose, so you're not left with a hose with fecal remnants and sewage smell inside for storage.

For the record, gray water is gross, but it's a bit less disgusting and less harmful than black water.

(There's no doubt that grey water is gross and stinky. Therefore, I always carry a gallon of water in my storage bay if there was no rinse water available when I dumped. It came in handy more than once!)

Campsites arrow sign handwritten


Two types of wastewater are created by using a camper: black and grey water.

They are usually captured and stored in separate tanks.

What is black waste water? Black is toilet wastewater containing sewage and carry disease-causing bacteria. It comes from flushing toilets in your recreational vehicle.

What is gray water? Grey water comes from your RV drains. It is created when you use washing machines, wash dishes, shower, use a dishwasher, or wash your hands.

The big difference between greywater and blackwater is that blackwater contains fecal matterโ€”IE, more bacteria and pathogens than grey.

Both gray and black water should be dumped into a proper sewage receptacle after your trip.

Enjoy your trip, and here's to no wastewater spills!

Kelly Headshot

I dedicated myself to living the full-time RV life for over 6.5 years, immersing myself in the unique quirks and joys of the boondocking lifestyle and gaining a wealth of knowledge and experience along the way. In December 2020, my business partner and I made the transition to part-time RVing, but in January 2023, we hit the road once again, this time in our trusty vans. My mission is to help others embrace the RVing lifestyle with confidence and excitement, armed with the knowledge and resources needed to make the most of their adventures. I believe that the more you know, the more you can truly appreciate and enjoy the freedom and flexibility of the open road.

  • Thank you for this info as Iโ€™m buying my first RV tomorrow morning (completely original excellent condition 1974 Dodge coachman 20 footer) or because my fiancรฉ of the last decade just passed away in a horrible accident and June has been our passion to always one day get an RV and drive around all of North America so in remembrance of her, I just have to do it and go full-time in Living life, so thank you for any advice you can give. She also wanted to start her own YouTube channel, so stay tuned as I may be documenting my journey shortly under the user name, JackTrippa on YouTube.

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