Hey lazyweb – anybody know if someone’s looked rigorously at the question of greywater use in the context of a Jevons-like paradox?
Putting together some notes for a talk this weekend to the Xeriscape Garden Club of Albuquerque (Sat. 10 a.m. at the Garden Center if you’re in town), I’ve been thinking anew about the question of greywater use – running a second plumbing system from the sinks and other non-poopy waste producers in your house out to the garden.
It seems obvious that this is a winner, because you’re making use of the wastewater rather than just throwing it away. Except that in many settings, it’s not thrown away, but rather returned via the sewage treatment plant for use by others. Here’s the new National Research Council report on reuse:
[E]xtensive reuse has the potential to affect the water supply of downstream users and ecosystems in water-limited settings.
The NRC is talking about larger-scale reuse, but the principle is the same. If you’re on the coast, and your sewage outfall goes directly into the ocean, greywater reuse seems like a no-brainer. But in desert communities like Albuquerque, it’s a more complicated question. My sewage goes back into the Rio Grande, where it is used by others. A gallon I divert from my wastewater stream to water my garden is one less gallon we remove from the Rio Grande at the north end of town, and one less gallon we return at the south end of town. There may still be good reasons for doing this – energy, system losses, treatment costs, etc. But “saving” that gallon of water is not one of them.
So here’s the Jevons question. For those not familiar, in brief, the Jevons paradox is the notion that, as energy technology gets more efficient, rather than simply dropping our energy consumption, we at least in part do more of whatever it was we were doing with the energy. So as lighting got more efficient and therefore less expensive, one of the things we did was light up a lot more of our spaces.
What if, by using greywater, I figure that since I’m using water that’s kinda “free” in the context of both money and supply, I figure I can use more in the garden?