SKB Hi, I rust blue 700 plus barrels a year as well as some browning work, when my grandfather worked in London they used the tap water it was very hard and they used to add water softener, when he moved out into the country he used water from a well and said it was superb for the work, I collect rain water in water butts that are all linked together, I have some barrels that come out on the first pass with grey patches I originally thought it was the water but then relised I did not have the problem with my brown barrels, by the time the barrels are finished there are no marks at all, I have been looking into this so I checked the guttering that supplied the water butts its was full of muck so I cleared this, then I emptied the water butts there was a lot of muck in the bottom which was oily to touch I have cleaned these out and clean them out regular as possible I no longer have a problem with these marks rainwater is fine and if you can set up a filter system even better, I dont think you need to buy in water also try the tap water with some softener.
