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.
Any. Any increase in copper exposure is dangerous to these patients.