I don't have much choice, the tap water has an EC of between 8.5 & 13 so its impossible to use that. i could get water delivered by the lorry load but would have to keep it in the tank with the rain water catchment. alot of hydro guys use RO(reverse osmosis)water which also has no calcium etc. So i thought rain water is fairly similar RO water has EC 00 my rainwater EC 0.1. I use Uv sterilization light to permantly alter DNA of bacteria to stop it reproducing. I don't know what else to do.