Well I'm going to go on a bit of a rant here... so bear with me
I'm really disgusted with the "need" to conserve water, our city leaders tell us to conserve water conserve water, yet they have zero problems with building all sorts of new housing, allowing population levels to soar (because that's all money!) yet as population grows, mother nature doesn't magically make more water available. Sure there's a shift from year to year but this is a problem that can not be fixed by conserving, because lets say everyone does conserve, what about 10 years from now when there's more people using that water? We're already conserving as much as we probably can, but gotta tighten the belt more, and more and more. It's a vicious cycle that can't be fixed through conservation efforts.
Now what to do with that water? Well lets say you let the city take care of it by dumping it in the sewers, our treatment plants filter it and screen it, and while I wouldn't want to drink it as such it's more or less clean enough for the environment. Now what does a city like San Francisco do? It dumps it out in the ocean, and they are literally wasting all that water because now it's gone. I believe in SoCal they're even talking about using that treated water, and sticking it through some additional filtration and putting that back into the mix as usable water. Personally I say we put all the treated water back where we got it. Or maybe someplace else in the mountains, mother nature is the best filter there is.
Ok enough ranting
My "waste" water goes to my garden, that means I don't have to water as much as some people might, others have mentioned using it for laundry, it's perfectly good water, hell it's perfectly safe for consumption too probably cleaner than what came out of your pipes in the first place since it went through other sorts of pre-filters. So if you simply plumb your "waste" line into your sewage then yeah you're wasting all that water. Hell I'm thinking of using my 300g rubbermade for the waste water (until I can turn that into a fish tank
) it has a hole low, I can plumb in a gate valve, cover the top to keep mosquitos down, hook a hose up and then go around my yard watering everything.
KatiAni systems are good too, it's basically just the prefilters plus the DI part, and the resins are separated so you have to recharge them, I thought about doing that for a while as well (plus you make water so much quicker!) but you have to be careful about the recharging process as you need a strong acid to recharge one, and a strong base to recharge the other. Muratic Acid is what's commonly used I believe, and you can pick that up at a pool supply store, Red devil Lye I believe is the other one, however I don't think they make that anymore, and I'm unsure what the active ingredient that gives it the kick that you need (Sodium Hydroxide?) but I remember looking in Lowes/Home Depot for a suitable replacement but I couldn't find any, of course I didn't try that hard to find it.