(This is the third post in a series about ways in which renters can reuse greywater. For a definition of greywater, and why it’s a good idea to recycle it, check this out. Here are links to the other posts in the series: 1 , 2)
Irrigating with Greywater
The daily volume of greywater produced by the average American (31 gal) is enough to irrigate about 227 square feet of growing space at 1/4 inch of water per day. That’s considerable area, especially on an urban lot!
But if you’ve created a system for collecting greywater (as suggested in this post), and want to start using it for irrigation purposes, don’t just start throwing buckets of greywater onto the vegetable garden. A more sanitary use involves applying greywater to pits filled with organic matter.
Manual Distribution to Mulch Basins
Most renters don’t have the luxury of implementing a fully integrated greywater system, so in lieu of a gravity fed distribution setup that passively conveys greywater from sink to landscape, we get to stay in shape by lugging buckets full of water to mulch basins. (Call the exercise a stacked function!)
Mulch basins are trenches, swales, or pits dug 6-12 inches deep and filled with a course, carbonaceous mulch material, such as woodchips. When greywater is poured into a mulch basin (as in the photo to the right), it is simultaneously purified by billions of micro-organisms, and infiltrated into the soil, which acts as another fine filter before the water reaches an aquifer or surface water body. Placed adjacent to (hopefully edible) trees, shrubs, and beds, mulch basins offer an abundance of year-round moisture that plants are able to slurp up before it sinks into the subsoil. All of this water that would normally go into a sewer or septic system.
If you’re a renter who is allowed to dig (or you’re willing to take a chance), it’s easy to dig one or more mulch basins to handle all the greywater that you’re not using to flush toilets. If you also have the landlord’s permission to plant, place shrubs and trees adjacent to the basins, where they can make use of the abundance of water. Try species that begin to fruit in the first year or two: raspberries, blackberries, currants, and asian pears come to mind.
To mitigate contamination from soaps, bacteria, and other potentially harmful substances found in untreated greywater, mulch basins (much like septic drainfields) should be located well away from surface water (ponds, streams, etc.) and wells.
And on that subject, here are a list of ingredients to avoid in soaps, detergents, and other cleaners that will end up in the water that goes into your mulch basins, or anywhere else in the landscape:
- Chlorine or bleach
- Peroxygen
- Sodium perborate
- Sodium trypochlorite
- Boron
- Borax
- Petroleum distillate
- Alkylbenzene
- ”Whiteners”
- ”Softeners”
- ”Enzymatic” components
[source: State of California Department of Water Resource’s Graywater Guide]
Vegetables and Greywater: A Worthy Adventure?
There’s much debate as to whether or not it’s safe to irrigate vegetables with greywater. Some sources say that it’s a sure way to get sick, while others say it’s harmless. In regards to vegetables, greywater guru Art Ludwig weighs in with the following rule of thumb:
[...] use grey water first on ornamentals, then on fruit trees, and then use the fresh water you saved on veggies.
But goes on to say:
In the past I have categorically recommended against using grey water for irrigating vegetable gardens. As a certain fraction of grey water users have always and will always do it anyway, I’ve decided to illuminate the boundary between responsible resource reuse and reckless public health threat in this area. Also, after irrigating veggies with greywater myself, I understand the attraction better.
As far as I could tell, nothing on the website does illuminate the boundary between responsible and reckless reuse, but he does list the following precautions to take when using greywater to water vegetables:
- Don’t put anything nasty in the water in the first place!
- Don’t splash the greywater on edible parts of the plant.
- Wash the vegetables thoroughly.
- Don’t eat them raw.
- Don’t get sick even if you eat something nasty.
[source]
That last one, obviously, is somewhat of a joke, but he throws it in there. He also adds that you should always wash your hands after greywatering.
Do What Works for You
Regardless of whether or not you end up irrigating vegetables with greywater, try a mulch pit. And if you don’t have the space for that, try the methods described in the previous posts in this series (1 , 2)
For more reading on these subjects check out Art Ludwig’s Create an Oasis with Grey Water and Brad Lancaster’s Rainwater Harvesting for Drylands Volume One, and Volume Two.
If you’ve already tried some of the methods described in this post, or anything else similar, what has worked? What hasn’t?
Tags: greywater, irrigation