The current problem in Flint was caused by the Flint River being more corrosive than Lake Huron, not by lead contamination at the water source. The reason lead testing is done in houses instead of just at treatment plants is to make sure that even the water in houses with lead solder is safe.<p>&gt;[...] houses built before 1987, when lead was banned for use in water pipes, often had lead solder joining copper pipes in home plumbing systems. In houses built before 1983, the solder has had time to build up a mineral coating that keeps lead from seeping into the water; in homes built between 1983 and 1986, seepage could occur, so the EPA orders regular testing of their water. [0]<p>[0] <a href="https:&#x2F;&#x2F;www.washingtonpost.com&#x2F;archive&#x2F;local&#x2F;2004&#x2F;04&#x2F;04&#x2F;wssc-lead-tests-clear-127-of-128-md-homes&#x2F;fe3d3a17-3bc9-4de7-a9ba-299d6edb436d&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.washingtonpost.com&#x2F;archive&#x2F;local&#x2F;2004&#x2F;04&#x2F;04&#x2F;wssc...</a>