Had a notice a while ago from the water board saying they were going to flush the main pipes where I live as part of a maintenance programme as they had not been done for years and they need to do it etc etc it was a nuisance with the water being off for a day but I thought I'd check my tds from the tap the other day and its down from 350 to 146 and I live in a hard water area. Anyone else had this? I guess it just goes to show how much gunk builds up in the pipes over the years