Maintenance and Repair: Responsibility of Private Water Lines

My question involves real estate located in the State of: Michigan

I own an irrigation well which was once used as a community well with several neighbors as a primary water source. Each neighbor connected to city water before we purchased our property, but the well lines still travel to each property where they have been capped. The system developed a leak on a neighbor's property and started flooding their yard when I turned the pump on for the season. They insist that the leak is my responsibility, but won't grant me access to inspect the leak. I have been advised (by local inspectors/plumbers/code enforcers) that private plumbing on their property is their responsibility. There is no recorded well agreement; it seems any agreement would have been verbal.

Also, they had excavation work done around their home in the months prior to all of this, and it seems reasonable the contractor may have damaged the pipe. The line would not have been marked by the public service, and it's doubtful they warned the contractor about the pipe because they don't use it. If they broke it, I believe they should fix it, but I don't know how to prove it. What can I do?

Maintenance and Repair: Responsibility of Private Water Lines