Thats a wonderful and very helpful post thankyou very much. I've copied it to read several times and let the details sink in.
The comments about the correct calibration of meters was also handy to know as I will be getting a meter as soon as poss.
I'd been reading some info from the water company here but as its in techno Dutch its slow going but your post in english will help me understand better what I'd been reading earlier. So another big thanks Horsemanrocks