The grand-prize winner of the TreeHugger/Popular Science/Instructables Go Green! contest presented an innovative solution to the evergreen problem of conserving water: A hydroponic bog garden that recycles the water from a sewage tank and produces a water effluent clean enough to discharge into surrounded ponds, ditches, and waterways—or even for irrigation.
An essential component of the bog is alfagrog, a highly porous volcanic rock with plenty of surface area, that houses colonies of bacteria that are responsible for filtering and cleaning any water that passes through. (Koi keepers love this rock because it keeps their fish happy, which means that they're happy. You wouldn't expect all that happiness to come from a humble rock but you see, it happens.)Because the bacteria in question are aerobic in nature, meaning that they need oxygenated conditions to survive, our bog makers had to add a compressor and rubber aerator to dissolve oxygen into the water coming from the nearby sewage tank. Add several herbaceous, moisture-loving plants, and voila, you have a bio-filtration system you can even fill up with wriggly, happy fish.
Okay, so it's slightly more involved than that, but we'll defer to the experts for the details. Step-by-step instructions, complete with pictures can be found at Instructables.com. Congratulations, Biotank! ::Instructables