it depends what that 003ppm or 012ppm is made up of - certain minerals will be more visible than others
thats true
and thats why I've said 010 (max) and I have absolutely no problems with it. Infact my new 4040 ro produces 005 before di and so if it stays that way I wont buy new resin when I finally exhaust it, why bother ?
I dont advertise that I use pure water (no breach of trade description there

) if a windows clean thats good enough by anyones standards , well my customers anyhow.