Here is a basic intro to greywater.  For more info read: "Create an Oasis with Greywater" by Art Ludwig, 5th edition 2009 or go to  

Lake Burera, Rwanda

Greywater is all the water generated in your house from bathroom sinks, kitchen sinks, showers, laundry.  This makes up 50-80% of our household waste water (Ludwig 2009).  The other percentage comes from flushing the toilet, and this is known as blackwater.  I'm going to focus on greywater right now and leave blackwater, living machines, composting toilets, and Watson's wick for another time.

Sink at Groundswell, Invermere, BC

Instead of thinking of greywater as something we want to flush away as fast as possible, we can see it as a resource.  Greywater can add extra productivity to our living landscapes.  Properly designed and maintained greywater systems also allow water to be treated and reused instead of polluting the surrounding area, especially in areas where there is no septic or municipal sewage.

Some benefits of greywater:
  • reduces use of clean water, if you are reusing your greywater to irrigate areas you would already irrigate
  • reduces strain on septic tanks and treatment plants
  • local groundwater recharge from additional water slowly seeping into the landscape
  • reclaiming nutrients from greywater into the soil
Greywater is another area where we can tweak our usually perspective and create abundance instead of waste- for example, watering an apple tree from greywater instead of losing all that water and nutrients.  Installing a greywater system not only creates a feedback system in our yard/garden, but also in our minds.  It allows us to think about what cleaning products we use, and pushes us towards conserving water.  It is also an excellent fit for cabins, tiny homes and human settlements that are removed from central systems of waste treatment and/or have limited resources. 

Solar Showers at Cougar Mt. Farm, Oregon, set up for a music festival

How does nature clean water?

Some greywater systems are set up to simply treat water and let it go (treatment/disposal), while others will integrate greywater into their perennial gardens to take advantage of the water (treatment/reuse).  If you are thinking in permaculture principles, you want to capture and store energy, and make the most useful connections from source to sink. Integrating greywater reuse into your system makes sense on many sites, but as always, it depends on the people and local conditions.

Greywater is cleaned by micro-organisms, plants and oxygen.  The easiest way to do this is to run greywater slowly through healthy soil.  A few points to consider:

  • Apply the greywater as close to the surface as possible, without creating contact points with people.  Ninety percent of the soil life is within the top foot of soil.
  • Create lots of contact time with bacteria and plant roots (slow flow is better than fast).
  • Have lots of micro-surface area (surface area means more bacteria and plant roots contact).
  • Design your system so that moisture, oxygen and nutrient levels that support survival of roots and bacteria.  (ie- the system doesn't spike, dry out or stay excessively wet so it excludes life).
  • Choose appropriate plants for your design.  Some plants thrive in wet conditions, while others do not. 
  • Treatment is more effective in warm conditions.  Bacteria and plants are more active in warmer conditions.
Wetlands- one of nature's ways of purifying water

Site Assessment

Like any system- greywater can be as simple or complex as your needs and the conditions of your site.  A site assessment form is a good way to structure your greywater project.   Ludwig also has another great check list for a more in depth evaluation of your home site.
  • what are your water resources? rain water, spring, municipal etc...
  • what are you greywater sources?  What is the quality and quantity of that greywater?  Where are they located in your house?
  • what slopes to you have?  Greywater needs a constant downhill slope of 2% or 1/4" per foot
  • what is the rate at which water is absorbed into the site? (soil percolation rate)
  • what area do you have for treatment/disposal?
  • what do you have to irrigate? Are you going to irrigate with greywater, or just treat and dispose?
  • climate?  does it freeze, does it pour rain for 8 months of the year?
  • who is using the system?  who is maintaining the system?
  • are there regulatory/social implications of a greywater system?
  • cost/benefit analysis

I'm going to focus on a few of the simple designs for a household such as landscape direct, drain to mulch basin, laundry drum to mulch basin, and the general idea of a distributed greywater system.  There are great designs for larger institutions and for specialized permitting and reuse, but I'm going to omit these here.

Buckets full of soap laundry water = one source of greywater at Agahozo Shalom Youth Village  which are dumped in the greywater planting of taro, papyrus, comfrey and mint


Greywater sources, quantities and qualities

Ludwig estimates that without water conservation, most people use 55 gal/ per person/day.  With water conservation fixtures it is around 40 gal/ per person /per day.  For households that have to haul water, it is more like 5-10 gallons/ per person/ per day.   You can do a more in depth analysis of your greywater sources using the following table, pg 10 of Create an Oasis with Greywater. Ludwig's table indicates the source of greywater (washing machine, kitchen sink etc), quality (concentration of soap, solids, salts etc) and quantity per person per day. In addition, if you have any water metering data you can use this to double check your estimates or what your household uses for water.

The laundry water from the farm house is treated in a bamboo stand just below the house


Calculating soil percolation rate

After you know how much greywater you will produce, it is import to calculate your soil percolation rate so you know how your soil will handle water, and how big of a disposal/treatment  area you will need.

How to calculate the soil percolation rate:
  • dig a hole where you want your greywater to discharge
  • dig it 6-12" (15-30cm) deep (about the same depth as your greywater will discharge)
  • put a marked stake or a measuring tape attached to a stake in the hole.
  • fill the hole with water
  • time how fast the water drops
  • do this 2 to 4 times
  • when it drops the same distance, in the same amount of time, this is your percolation rate.  For example, if it drops 2 inches in 90min then your percolation rate 45min/in
  • if the water drops very fast, or not at all you might need to modify your greywater designs
Table 2.3 Disposal Loading Rates (pg.13, Create an Oasis with Greywater)

Soil infilitration rate, min/in Loading rate gal/day/ft2 Area needed ft2/gal/day
0-30 2.5 0.4
40-45 1.5 0.7
45-60 1 1
60-120 0.5 2

So for our example of a percolation rate of 45min/in, the loading rate is 1.5 gal/day/ft2.  So if we had a household of 2 people using approximately 55gal/per person/per day, we would need 0.7ft2/gal/day*110gal/day= 77 sq ft of treatment area for greywater.

These folks are digging a swale, not a percolation pit, but they are still hard at work


Surge/Basin Capacity

In addition to knowing how big your treatment area needs to be for the amount of greywater you produce, and the percolation rates of your soil, you also need to have an idea of peak flows. If you have a washing machine, bathtub and kitchen sink all draining at once, does your system have the capacity to handle that much water at once? For most homes, 45 gallons(170L) is sufficient.  This means that your system, for example, that the mulched basins and distributing pipes have at minimum 45 gallons (170L) capacity.

The Bull River surges in a narrow canyon, BC

Examples of Simple Greywater Designs

Right, I know, that was a bunch of numbers... on to some examples!


The classic and most energy intensive (for you) waste water system- but also highly effective, as the greywater can go to plants according to changing needs as you see fit.

If you have ever camped, you probably have done a dishpan direct to landscape greywater system


Shower in Perennial Planted Area

I have most often seen this in tropical areas, but also used in Canada in the summer.  Many work-exchange farms and homesteads have this set up for volunteers. It can be as simple as a garden hose into a shower area that is somewhat private, where the water run-off can drain to a clump of bamboo, some bananas, etc.  For warmer options, hook up your water source to some kind of solar collector.

A black hose on the roof of this cabin serves as the hot water for the shower on the left. Cortes Island BC
The shower drains directly to landscape, with a bamboo planting for a privacy screen and to absorb the greywater


Drain to mulch basin

Mulch basin is a simple and effective way to treat greywater.  You can plant the mulch basin with appropriate water loving plants or leave it unplanted.

The basin is dug 10 to 12" (25-30cm) deep and wide enough for the surge capacity (around 45 gallons) and also what you calculated for area needed according to your percolation rate.  You can have multiple basins, and I will touch on this later in the distributed system.  The basin contains the greywater and allows it to soak into the topsoil.  Filling the basin with mulch such as woodchips, increases micro-surface (for bacteria and root growth), soaks up greywater, adds more food for the soil food web.  You will need to top up the mulch over time as it slowly decomposes with all the biological activity.

You can plant your mulch in a variety of ways: some like a tree in the middle on an elevated island, some plant perennials around the outside of the mulch basin.  For tropical systems, bananas grow well in greywater systems. You can also plant citrus, mangos, avocados, but make sure to put them on high island. For more temperate areas, figs, clumping bamboos, elderberry, and willow do well in greywater. Some temperate fruit trees will also do well with greywater, but most will need to be on a high island so their roots don't get too wet. Any wetland/riparian plant in your local regions will also likely thrive with greywater application.

A mulched basin planted with taro and bananas at Sat Yoga, Costa Rica

Laundry drum to mulch basin

Laundry machines are relatively easy to re-plumb into a greywater system.  All you need to do is to make a place of the hose to come out of the wall/window and into a 30-55 plastic surge tank (to slow the flow of water) where it is then distributed to the landscape through a direct or movable hose. Note- the hose is not attached directly to the machine, because it could kink and then backflow into the machine.  It is better to have the washing machine drain via a rigid pipe into a barrel, and then drain the barrel into a pipe or hose to the landscape. You can also use the laundry machine pump to move water horizontally or a short distance vertically.  This would be beneficially if you want to irrigate an area that is upslope. 

You can see an example of this system in this video LA backyard homestead around 2min and 20sec.

Scouler's Willow, Salix scouleriana, bush on the right is planted in a wet area of the food forest, Creston, BC


Branched Drain Greywater System

A branched drain system uses branched pipe to distribute greywater to multiple mulched basins, that are typically planted.  This allows for the greywater to reach more areas for irrigation, and to reduce the issue of overloading one area with greywater.  This could be accomplished by multiple splits, or a valve that switches the flow from one area to another to allow for recovery. 

This is an image taken from the San Francisco graywater design manual which is an excellent guide to greywater, Note water is released under the cone shaped pots (can be a modified plant pot) to reduce direct contact between people and animals



  • Don't store greywater (more that 24 hours)-it will start to smell bad!
  • Minimize human/animal contact with greywater
  • Infiltrate greywater into the ground.  Don't let it pool or run off.
  • Keep it simple.  Avoid pumps and filters that need maintenance and will affect your system if they don't get regular upkeep.
  • Match plant irrigation needs with the amount of greywater the plants will receive.

If you have a greywater system used by many different types of users, it is a good idea to keep it as simple as possible and check it regularly.  This is the case with the Lost Valley Guest Kitchen greywater system.


Trouble shooting:

  • Smell- don't store greywater! Examine your system for any areas where water and solids could accumulate, widen the infiltration area
  • Grease- occasional pot of boiling water.  Grease you can do a grease trap, or increase the size of the infiltration area
  • Rainwater overflowing the basins in the rainy season.  Direct rainwater runoff elsewhere (catching it and using it would be best), or switch to a long swale style infiltration basin or constructed wetland if you are in a very wet climate. 

This is a constructed wetland for greywater that is purposely fed phosphorus
 (causing the algae to bloom) to enrich the water irrigating the plants

What about freezing?

There are several options for this:
  • divert your greywater into the sewer/septic for the cold season
  • divert the water into a greenhouse if you have that option and grow plants in the winter
  • in a well design system, no water should be pooling, so there shouldn't be any freezing in the pipes. Greywater is usually warm enough to melt any ice as well.  Having the outlet under mulch and snow would also likely create conditions where some microbial activity is still taking place.  The branched drain system has been tried in areas where it gets as cold as -20C.

Kokanee spawning at Kokanee Creek Park, BC Aug 2013


Some other considerations:

  • Although you could use greywater to irrigate vegetables, best practices is to avoid watering plants that you eat raw with greywater.  In addition, greywater application is more suited to perennial plants that you don't have to dig up and mess up the root system.
  • provide clean-outs and inspection access
  • map your system. It really is harder to find the pipes once they are buried!
  • consider adding diverter valves, to divert greywater to septic/sewer if your soil is waterlogged, frozen or the system needs repair
  • grease traps or filters- Ludwig isn't a big fan of them, but I have seen many systems with grease traps, especially those that collect greywater from kitchen sinks.  Most of the time they are just 5 gallon buckets where the grease can float up, and you take the water to the landscape from the middle of the bucket.  Filters and grease traps need to be changed and cleaned regularly, or else they will slow down your system.
  • use sanitary drainpipes and fittings because they have smooth turns (less chance for solids to get caught in corners, 11/2" pipe to 2" pipe the usual size for greywater)
  • use garden friendly soaps and cleaners. (avoid chlorine and boron, do not use cleaners that have salts)
  • If you are doing a retrofit, divert greywater downstream from traps and vents (this ensures that you you won't get gases from the sewer/septic from going into the house... if you have no connection to the septic/sewer then ignore, and just install a pipe outside)
Example of greywater plumbing with a diverter valve to sewer/septic
image from:

"In fact, as a species we are approximately 65 percent water-it defines and shapes us in every way imaginable, physically and spiritually, from our first few months in the womb, when we are literally enveloped by it, to life outside the womb, where we need to be constantly replenished with eight to ten cups of clean water each day to survive." -Jason F. Mclennan, CEO, Cascadia Green Building Council



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