A little digital ppm meter comes with it(that's what sold me, being a gadget freak), I get 160ppm out of the faucet (we have basement wholehouse 10-20 micron string filter, this helps the other filters last longer), 30-40 ppm form the Brita and 0 ppm from the Zero.
Ironically, coffee still taste better with the Brita, guess you need a little crap to help pull a good brew.
To get the point across about what is put in the local water supply, I used to do an experiment with the kids in my science class. .I would give them some local water that went through the Brita. Then I would give them the same water straight from the tap. The look on their faces was something to behold.
Actually, the more mineral filled the water is, the better the coffee. I think it has to do with the ‘crap’ clinging to the coffee grounds for longer and making a richer cup of coffee.