Last post from me on this subject, though a long one. I'd just like to fully lay out the water problem in my house, and hopefully somebody, whether a plumber or whatever, can have a clue what might be awry. Here goes.
For many years, we have had terrible quality mains water, slimy and containing sediment, which in turn would hasten us to clean the attic tank every few months due to sediment at the bottom. It wasn't until late last year that a breakthrough happened, totally by accident, when we were having our washing machine replaced. I detached the feeder pipe to the old washing machine and drained it at mains pressure for a minute or so before I replaced it with the new feeder hose to the new washing machine. Didn't think anything of it.
Suddenly, the water became much clearer and fresher than before out of the mains tap, noticeably so. Still not really up to standard, but much better to us at least. Within less than a week, it had gone bad again, you know always can tell in our house as the hot water starts to smell musty, and the cold water leaves your hands a little yellow! So I repeated what I had done before, draining out the WM feeder pipe at mains pressure into the sink. Same result, same cycle again.
I then had a leak detector come round, who assured us that he could not detect a leak... more frustration. I then had our local council, who regulate the water come round and flush the nearby hydrant. This they did, and the water became very clear for a couple of weeks before going back to a terrible state again.
On this group, it has been suggested to me that my house could be at a dip in the mains or a 'balance point' where we are in the middle of two seperate directional mains flows, each one bringing its dirt into the house.
I still flush out my system using the washing machine method, at least whenever it is absolutely necessary, and believe me, you know when you have reached that point. What I cannot get my head around is why this would be so effective (at least in the very short term), and why the water gets so bad so quickly. If we don't have a leak, I don't know why this works like this. The water is not supposed to be such a problem in the general area either, the council tell me they never get many complaints.
If anyone could shed any light on these ramblings, by all means, be my guest.