|Ignore the bucket in this illustration! See update below.|
Update 3/13/2011: I met Brad Lancaster last night and he told me that he and Art Ludwig no longer use the upside down bucket described in this post. The reason is that detergents can build up in the hole. In my experience the bucket was also an unnecessary step. While I have a clay soil, the hillside drains fairly well. A properly sized mulch basin should suffice to allow greywater to infiltrate. Also, the new generation of washing machines use a lot less water than the old one that I still have. Other than the unnecessary bucket and the persimmon tree (died, for some unknown reason) this greywater application has worked very well. Our fruit trees are lush and happy.
With the news that Lake Mead could go dry by 2013 we figured it was about time to figure out how to grow food with very little water in a Mediterranean climate that gets on average 15 inches of rain a year (3 inches last year). Our water worries sparked the beginnings of our draught tolerant mini-orchard. Thankfully greywater and some tough, water sipping trees make it possible.
Step one was figuring out how to reuse our washing machine water (read our earlier post on the washing machine surge tank we built). Step two was matching that washing machine water output to the right kinds of plants for the mini-orchard. We settled on the three “Ps” — pomegranate, persimmon, and pineapple guava, plus a mission fig tree to replace the substandard one we cut down (even though God Hates Figs!). The advantage with these four trees is that they can survive, once established, should we find ourselves unable to use any water due to the aforementioned bad-ass draught scenarios.
Our house sits on a small hill, with the front yard sloping down towards the street. We placed the trees at the top of the slope and made mulch basins like the one illustrated above.
The outlet chamber consists of a upside down three gallon bucket with a bunch of holes punched in it. The purpose of the outlet chamber, which is buried in the mulch basin, is to help the greywater infiltrate our heavy clay soil. To use it we simply place the hose coming from the surge tank into the hole in the top of the outlet chamber. We cover this hole with a brick when not in use. The photo below shows the digging of the mulch basin and the installation of the outlet chamber in progress:
The completed mulch basin and (hard to see) pomegranate tree to the right.
We used straw for mulch We use wood chips for mulch (replaced the straw):
These craptacular photos don’t show the details very well, but the mulch basins were dug in such a way to also catch rainwater as it flows down the hill. Both rainwater and greywater work their way into the soil and slowly move down the hill over the course of many months. Since installing the greywater system we’ve seen previously sad plantings we did years ago of rosemary, wormwood and Mexican sage thrive. And we’ve got lots of nopalitos coming our way from the prickly pear plants.
For more information on these simple, water saving strategies see Brad Lancaster’s excellent book Rainwater Harvesting for Drylands.