What is Greywater?

Living in arid regions of the world can be challenging for most gardeners. Depending on your region, months may go by without a drop of rain, yet many of your plants will still need water to thrive. Here in San Diego, we may go 6 months between rains and typically, like all Mediterranean regions of the world, the dry season is also when it is the hottest and most plants really want some extra water. There are many strategies for landscaping and gardening in the drier parts of the world and many of them address techniques to conserve water and minimize evaporation. Greywater is one strategy that can be quite effective in providing year round irrigation in arid regions.

What is greywater?

Greywater is any freshwater used in the daily household activity that originates from the shower, bath, sinks, and washing machine.* Basically, any water used in the house that does not come from the toilet (used toilet water is called “black water”). Think of it as lightly used water with a few added nutrients. This water can then be reused for things like flushing the toilet or irrigating your landscape.

Why use greywater?

A recent client's laundry greywater is used to nourish and water this Horsetail and Banana basin

There is an axiom that that I once heard that says, “It is not how much water you have, but how many times you can use it that matters.” To me, this is why I view greywater with such importance and opportunity. It represents a simple way that I can double my water efficiency. For example, let’s say that I use 100 gallons of water to shower in a week. If that is all I use my total use of that 100 gallons is the same, 100 gallons. But, if I then take that same amount of water, shower with it and I use it afterwards to irrigate my garden then I am essentially doubling my use of that original 100 gallons. In this way I am getting 200 gallons of use out of only 100 gallons of water! I like to take this a step further and not only use greywater to irrigate my garden, but use it to grow fruits, nuts, and other perennial food plants. In using greywater in this fashion, I believe I can get another 100 gallons of regional water savings per 100 gallons used in the shower because that is 100 gallons that a farmer is not having to use to grow the food that I am eating. In that way, I can use one amount of water and get triple the value!

Here in San Diego, the average resident uses over 150 gallons of water per person per day. Half of that water goes to irrigate the landscape while about while nearly another third is used inside the home from sources that could be reused outside. Think about that for a second. This means the water we typically use to shower and wash our hands or clothes is just about how much we could use to irrigate the average landscape. Combine this with other water conservation strategies like mulching, using water appropriate plants, and rainwater harvesting we can potentially eliminate irrigating with virgin freshwater ever again.

The author setting up a laundry-to-landscape greywater system

Choosing a greywater system that works for you

There are many factors involved in choosing a greywater system that works for you. I have highlighted a few that can impact the overall system design:

Three-way valve diverting greywater from a washing machine to the landscape.

  1. Budget
  2. Access to indoor plumbing
  3. Laws and regulations
  4. Soils
  5. Topography
  6. Level of dedication

1. Budget

It is important to initially identify your budget on what you are able to spend on a greywater system. There are systems like putting a bucket under the sink that can be almost free to those that can be fully automatic and run into thousands of dollars. The more money put into a greywater system does not necessarily mean that it is a better system. Simple, low-tech systems can often last longer than the pumps, filters, and other bells and whistles found on high-tech systems.

2. Access to indoor plumbing

Is your home built on a cement slab with the plumbing pipe buried in it or do you have a crawlspace or other feature that enables you to gain access to the waste water pipes? This will not only greatly change the cost of building a greywater system, but if your pipes are buried in cement that might make it next to impossible to install a greywater system. However, even if your house sits on a cement slab it does not mean that you cannot install a greywater system. A washing machine or sink that that sits on an exterior wall can often be used. If that still doesn’t work and your climate permits, you may just move your plumbing outside in the form of an outdoor shower, sink, drinking fountain, washing machine, etc.

3. Laws and regulations

"Here in San Diego, California, residents can install a greywater system from a washing machine with no permit needed as long as there is no pump installed."

Each state can regulate greywater to either allow for it or not. Furthermore, each city tends to further regulate or deregulate the legality and system design components needed. Here in San Diego, California, residents can install a greywater system from a washing machine with no permit needed as long as there is no pump installed. However, installing a greywater system from a shower or bathtub requires a permit. Permits will most always add to the expense of any system. Greywater laws in Arizona allow you to install greywater systems from just about every source of greywater in the house except for the kitchen sink and toilets without the need for a permit. It is important to know the laws and regulations, but in some cases you may be able to skirt the local laws and regulations by looking for items that are allowed. For example, while in San Diego, I may be required to get a plumbing permit for an indoor shower greywater system. However, if I happen to build an outdoor “water spigot” that is attached to a shower head in an area that needs water there is not a law that requires a permit so far as I can find in the regulations. I can even have that outdoor bathtub included privacy screens without the need for a permit.

4. Soils

It is important to know a bit about the soils that you will be discharging the greywater into. Clay soils drain much slower than sandy soils. With any greywater system, we do not want to have ponding or pooling of water. This creates potential vector problems with mosquitos and other critters. The idea is that when discharging greywater into the landscape, we want it to absorb into the soil quickly. Designing a greywater system in heavy clay soils means that the discharge points need to be more spread out to keeping ponding to a minimum. Sandy soils allow for irrigating in denser positions.

5. Topography

There appears to be a general law of water that states, “Water moves downhill unless it is following money.” Meaning water moves with gravity unless money is paying for pumps and power. Using greywater from the house to irrigate plants can be easy. If the area to be irrigated is uphill from the indoor greywater sources then a pump will be needed to get the water to that point. If the irrigation zone is downhill then gravity can do the work for you. My preference is almost always with gravity as it does not ever break, fail, or take time off.

6. Level of dedication

How much time do you want to put into maintaining and operating your greywater system? A system with a bucket under the sink, while inexpensive, will require nearly daily interaction to keep it working. Heavy buckets of water will need to get dumped every day. A system with more permanent plumbing may not require any interaction at all other than the occasional maintenence. Any system with pumps and filters typically will require higher maintenance than those without such features.

Greywater Compatible Soaps

It's very important to know what goes down your drain. Your greywater feeds biological systems and too many salts or harsh chemicals will disrupt, setback, or kill those living creatures. Look for soaps labeled 'biodegradable' or 'biocompatible', but still exercise caution be reading the ingredients label. The Ecology Center has a good list of greywater ingredients to avoid. The following are soaps that we recommend for greywater systems:

Laundry Soaps for Greywater Systems

All-Purpose Soaps for Greywater Systems


Greywater can be a great way to irrigate your landscape and cut your water bill at the same time. Greywater systems are varied in cost, legality, ways to install and maintain. To learn more about greywater including information on soaps to use or avoid, building a simple greywater system, and other topics stay tuned as we demystify the world of reusing household greywater through future blog posts.

Download our Laundry-to-Landscape Greywater Diagram for free!

Download this helpful diagram showing how a laundry-to-landscape greywater system works. Note: periodic cleaning of ball valves is essential to avoid clogging and you will also want to leave a 1" end point un-valved incase valves upstream do get clogged.

*Greywater is also spelled graywater. We choose the english spelling of “greywater” because Art Ludwig, author of An Oasis with Greywater, uses it and his book is an excellent resource for greywater systems.

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