I lived in Perth.
The water from the tap is ok to put straight through a system,my brother in law uses one for car valeting purpopes....but what you have probably been told about is what they call bore water which is basically water pumped straight from the underground water table.It comes up in WA as a thick brown/red crappy colour,stinks to high heaven as well sometimes,this would probably ruin any form of purification system in no time at all.
Over in WA they have deslination plants to convert sea water as well,i think they are down near rockingham somewhere..