Silly me thinking that since hydroponics has the word "hydro" in it, that it must be water intensive.
Also in my late night research I found a two interesting vague references. One to using worm casings (aka fertilizer produced by worms) as nutrients for hydroponics. The other to using a sand filter and UV light to recycle the used water in a hydroponic system.
Seems like an interesting technique for gardening in arid conditions like Los Angeles.
I almost have enough motivation to move some furniture around so I could set up two small hydroponic flats. (One using commercial fertilizer and the other vermicompost derived.)
Also I this seems like it might be useful for growing things in a condo, which is useful because houses with dirt around them are incredibly expensive around here.