Living in a dryland, one of my goals is to capture and reuse as much of my “greywater” as I can, here on my property, "Dolce Verde" in the middle of Phoenix's downtown Historic District.
What is greywater?
Greywater is water that has already been used for one purpose but is clean enough to be directed into the landscape. Sources of greywater in your home include:
- Bathroom sinks
- Washing machine
Note that kitchen sink water is considered “dark grey water”. This is because kitchen sink water often includes things like grease from washing dishes or harsh chemicals such as cleaning supplies, or other things people put down sinks like solvents (paint thinner, etc). While kitchen sink water can be used as a resource, you have to manage it more closely than other sources of greywater. And you definitely need a jandy valve – a valve that will allow you to switch from venting the water from your landscape to your sewer and back again, to control the water quality that goes to your landscape.
Toilet water is considered “black water” due to public health concerns with human waste products. The best way to handle toilet water is to get (or make) a composting toilet. There are sleek models for inside the house or versions for outdoor models you can build yourself.
So back to greywater.
One of the common problems of greywater is access – how do you get it from inside the house to the landscape?
In my case, my bathroom shower/tub was located on an outside wall, but on the other side was a screened in back porch with a cement slab floor. It would have cost a lot for me to retrofit the indoor shower to vent to the outside. So I decided to turn this problem into a solution and create a fabulous outdoor shower. It’s piped for both hot and cold water and the weather in Phoenix makes showering outside possible all year ‘round. I think I’ve used my indoor shower less than a dozen times since this project was completed in May of 2008.
With greywater, you want to immediately direct the water into an area where it can soak in – you want to avoid storing greywater or directing it to a place that has poor drainage. Always do a “percolation test” (or “perc test”) on your soil by digging a hole about a foot deep, filling it full of water, letting it drain, filling it again and then seeing how long it takes that water to completely drain from that area. If it drains in under 4 hours – you are good to go. If longer, your soil needs work. Consider a different spot.
Using the perc test, we determined that even though I have fairly heavy clay soil, the “perc rate” was adequate for the amount of greywater that would be generated for 2 people taking daily showers of about 5-10 minutes. We designed the shower to have three drains. Each drain feeds an infiltration pit. The idea is that you block off two of the drains with rubber drain covers each time you shower, leaving the third open. The next person to take a shower, moves the drain covers according to a predetermined plan. It’s easy to water some plants more with this system, if say, you have a higher water use plant that will need extra water.
This greywater portion of this project was led by Brad Lancaster, author of the bestselling “Rainwater Harvesting for Drylands and Beyond, Vol. 1 and 2”. These books are invaluable to any water harvesting endeavor. You can find them in my shop.