Question: What Exactly Is Grey Water?

We often hear about water conservation and the importance of using less water in this day and age.

woman hands doing dishes

Especially for homesteaders or anyone living in a place where water is scarce and precious, the pressure is really on to get as much “mileage” from your water as possible.

A method that is commonly recommended to this end is the reuse of gray water. But what exactly is gray water? 

Gray water is simply household wastewater that is not contaminated by urine or fecal matter. This can include water from baths, showers, hand washing, laundry, and dishwashing.

Basically, any water that doesn’t come into contact with human waste can be considered gray water, and it is possible to reuse this water for other chores both in and out of the house for a variety of purposes.

With some smart engineering and an eye toward sustainability, you can separate and even store gray water in day-to-day use so you don’t have to waste your fresh, potable water on lesser tasks. If that sounds interesting, keep reading: we will tell you more in this article.

Gray Water is Wastewater, but Not the Worst Wastewater

The first thing to understand about gray water is that collected properly, it doesn’t contain human waste.

So long as the wastewater from your sinks, dishwasher, tubs, and other such drains is not allowed to reach the main sewer or septic pipe in your home, it won’t have any opportunity to come into contact with poop or pee.

Wastewater that is contaminated with either, in any quantity, is known as black water and is not something you want to be messing with for any other purpose without heavy treatment. That’s a topic beyond the confines of this article.

Gray water, on the other hand, is generally safe to handle (or at least much safer) and can be used for non-potable purposes so long as it isn’t for human consumption and won’t come into contact with food. More on those purposes in just a minute.

Gray Water Can Still Contain Lots of Germs and Bad Stuff

Don’t misunderstand: gray water is still contaminated with all kinds of stuff.

For instance, water from laundry will have soap or other cleaning agents in it, while water from the kitchen will certainly contain food particles, grease, mold, and the like. Anything that goes down these drains will be in the water!

As a result, gray water should not be used for drinking or cooking purposes, and you should be careful about contact with gray water if you have any open cuts or wounds.

In general, it is best to be cautious and assume that all gray water is contaminated with germs to some degree. Avoid contact with your eyes, mouth, or any open wounds.

6 Uses for Gray Water

While the idea of using gray water may sound a bit icky at first, it actually makes perfect sense.

After all, this water is not contaminated in any significant way and can be perfectly safe to use for all kinds of things.

It isn’t wrong to think of water in this category as “lightly used.” It’s still good and does not have to go into the sewer or septic tank just yet!

Consider the following uses for gray water around your home or homestead:

1. Watering the Lawn

Most gray water is nowhere near contaminated enough to pose a risk to your grass or other ground covers, and some of the “contaminants” for us can actually serve as nutrients to your lawn.

If you have a large lawn, you’ll need to pipe the gray water into a receptacle and then hook up a hose to water normally, but this is a small price to pay and one that can save you a bundle on keeping your grass green and happy!

2. Watering your Garden

Just like your lawn, there is no need to worry about using gray water on your garden.

In fact, many plants will actually benefit from the extra nutrients found in this lightly used water.

Compared to watering the lawn, you can make easier use of gray water in a watering can for the task. As always, make sure to wash any harvested fruits or veggies with fresh water prior to eating them!

3. Watering Ornamental Plants

So long as the ray water does not contain harsh chemicals, you can use it for watering or misting any decorative plants you have inside or outside.

4. Cleaning and Rinsing Vehicles

Washing your personal vehicle, boat, ATV, and other big-ticket purchases use a ton of water.

Offset some of these costs by using gray water if you can, and save the fresh water for the final rinse.

Simply collect the gray water in a bucket for scrubbing or else use your hose with it if able. Not only are you saving water, but you’ll be pleasantly surprised at how well this works.

5. Cleaning Exterior Surfaces

In most cases, you can use gray water for exterior cleaning. This includes cleaning the outside of your home (windows, siding, etc.), washing the deck, sidewalks, pavers or patio furniture, and even power washing the driveway.

You’ll want to use a little more caution here, as some cleaners that might be present in gray water can cause fading or other damage, and any “chunky” debris can clog sprayer equipment.

But aside from this drawback exterior cleaning is a wonderful way to save on what is ordinarily a pretty fresh water-intensive task.

6. Flushing the Toilet

In an emergency situation where your usual water supply is shut off or intermittent, you can load the bowl and tank of your toilet with gray water and get it to function, and flush, normally.

You don’t need me to tell you what a valuable asset this can be in any crisis situation!

Instead of squandering your precious fresh water under the same circumstances, let your gray water supply take the hit. Trust me, it beats using a camping toilet for the duration.

As you can see, there are many excellent ways to put gray water to use around your home.

What You Definitely Shouldn’t Use Gray Water For

Gray water is very useful, but you shouldn’t use it for some things, namely the following:


I hope this is obvious. Gray water contains too much contamination for drinking without serious purification.


In a similar vein, you don’t want to bathe with gray water. Harsh chemicals, food debris, and abundant bacteria are not going to help you get very clean.

Wetting Animals

Again, gray water contains stuff that can be harmful to skin, hair, and fur, so you don’t want to use it to cool your animals. They might wallow in mud, but at least that doesn’t have harsh chems in it!

Collecting Gray Water

For many homeowners, the single biggest challenge associated with using gray water in their weekly rounds is simply collecting it in an easy and logical manner.

Most people think of gray water collection as manually scooping it up or out of fixtures with buckets or bowls and storing it, somehow, until it is needed. That is one way to do it, but it doesn’t have to be “the” way.

How to Recycle Waste Water Using Plants

Gray water collection is made much simpler via modification of your existing plumbing or intelligent installation of the right things when plumbing is first being installed.

One of the easiest ways is to just re-route the discharge line of your washing machine into a dedicated holding tank.

These are available commercially, or you can make your own out of a repurposed rain barrel or other food-grade containers.

Showers and sinks alike can be fitted with “three-way” diverters that can route wastewater from one drain- to the main sewer/septic line- to another, in this case, your gray water storage tank.

It’s really not as difficult or complicated as it might seem at first blush, and the benefits in terms of both water conservation and convenience are more than worth the effort.

These installations can be as simple or as sophisticated as you might like depending on your budget and your own level of do-it-yourself expertise.

It is possible to have storage tanks with overflow and backflow protection, powered pump assemblies, and even options for supplying exterior spigots on demand. Pretty cool if you want to make gray water use a part of your life.

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1 thought on “Question: What Exactly Is Grey Water?”

  1. For those on septic systems there are other benefits to repurposing grey water. For one, catching the water before it reaches the septic tank takes the added load off that tank. Without the added incoming water, the system will have more time to decompose the tank’s contents before the effluent gets pushed out to the leach field. The cleaner the water is when reaching the leach field, the longer the leach field will last. The other upside is that if you can divert your washing machine to a grey water outfall, the septic tank will not have to deal with the large and sudden inrush of water (explained above), the soaps, and the bleach, the latter of which will KILL the enzymes that are essential to proper septic tank operation.

    My grey water outfall from the washing machine simply dumps into my lawn. Any little bit helps in the desert. If needed, that water could be rerouted for other uses. During “good times’ though, I don’t want to deal with the complexities.

    One other thing I do is keep a 5-gallon bucket in the shower. This catches the “warm-up” water, usually about 3 gallons worth, thus catching the water before it even becomes grey. If needed this water could be consumed as long as the bucket is kept clean. During normal ops though, this water is better suited to watering the herb garden just outside the house. You’d be surprised at how much watering you can get done with three gallons of water! Catching “warm-up” water can also be done on a smaller scale in the sinks in your house.

    I disagree somewhat with filling the toilet TANK with grey water, as the contaminants in it can gum up the works in there, and ruin the flapper valve. Better and easier, just keep a bucket of water near the toilet. When you’re done… resting… just dump some of the water into the bowl to flush it. This also prevents the “aww-damn” moment; that moment when the toilet tank lid slips out of your hands and shatters on the floor! Be sure that after purging the bowl you pour in enough water to keep the water level above the bowl’s throat, as this is the bowl’s P-trap which keeps sewer gas from backing into the house.


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