What copper levels in drinking water are potentially hazardous for wilson's disease patients?

0.1ppm. Drinking water rarely exceeds 0.1 parts per million (ppm), deemed a safe level for wilson's disease. Testing is not so much for fear of exceeding 0.1ppm, but to make sure your home/school is not prone to excessive leaching (example: acidic water in copper pipes). Consistent levels <0.1ppm mean leaching is unlikely. Flushing copper pipes (let water run) is recommended before drinking/cooking.
Not a risk. If your Wilson's is properly managed, this will not pose a danger to you. This is my opinion. There's talk about 0.1 parts per million being a case of "I wonder why so much copper in the water", but there's plenty of copper in many foods and Wilson's folks really do not need to restrict diet.