I used a mixture of water from my water softner and 'hard' water I obtained from the tap using the by-pass valve on my water softner. I mixed at a ration to get a GH of around 3-4. The KH and PH were not impacted. My low light plants (Crypts, Anubia, Vals) did well.
I've sent switched to an RO/DI system, using Seachem Equilibrium to restore GH. This is even a better option.