Interesting about the Zero water. I didn't know about this. It's pretty expensive though, I read if your water is very dirty you get about 11 gallons out of one cartridge (not 20 as advertised), and it's $60 for a 4-pack.
The other one I posted about says you get 150 gallons per cartridge, which costs $40, even if you only get half that if the water is very dirty it's much cheaper at about 50cents/gallon.