copper sulfate is not good for the bacteria at treatment facilities, although a little here and a little there won't be detrimental to a wastewater treatment plant, but if everyone decided to treat their services with it on the same day, there would be an impact for sure.
We offer the product we carry to the customers in our district at our cost, BUT for the OP's situation I thought I'd offer it to try to help him get some more time before a dig, and that's IF they found tree roots were really the only problem. The product we carry can be bought on line as well, it's called rootx.
