I would consider checking your taps. Some of the old water systems don't get changed, and can carry large amounts of diffrent metals, along with large amounts of lead (from lead pipes.) I suggest possibly doing some tests on the water as well. I don't know what you could do, but you could try to take a few samples, and get one to a vet.
You could be getting somewhere, maybe the water companies slack. If you find anything take it up with your local government, and see what you can do.