Lol you guys are funny. Obviously clean water conservation is a very important topic. So if you wanna talk about water conservation lets talk about it.
The chemical issue is completely different, and you're very naive to think that the small amount of waste water that hydro growers may dump is a real issue. I gaurentee that the 1000+ acre farms all around where I live spray and dump more crap into the soil then I have ever put down the drain. There is no were near enough hydro growers( of any kind not just cannabis) to impact the water system anywhere near as much as commercial agriculture. Then you must give consideration to all the manufacting waste from factories, chemical plants, and other sources.
I'm not suggesting that we shouldn't all do what we can to improve the condition of this planet. We need to focus on the real problems, rather then make big issues out of minor things. Personally during the summer I use some of my left over nutes to water my veggies out side when I change my res. I also don't buy into changing my nutes every week or 2. I typically change my res once a month, and just top it off with water or nutes as needed in between, the plants grow great.