I do not give legal advice over the web, but I have outlined some issues you might want to consider.
1. I assume the bad neighbor's use started before you purchased the property. If the use was permissive, you may have the right withdraw permission. However, if the permission was oral, it may be difficult or impossible to prove.
2. If the use has been going on for 20 years or more, bad neighbor may have the legal right to access the well and use the water. There are other ways bad neighbor could have established legal rights as well. If the rights were acquired more than 50 years ago, your neighbor might have abandoned them.
3. You should should look at your title policy and talk with the good neighbor and the people who sold you the property to find out something about the history of this shared well.
4. Finally, you should do a title search on your neighbors to see if their titles have any mention of easements or other covenants regarding the well.
5. A well agreement can define the rights of access, but it may also determine cost sharing arrangements.
6. The only was to understand your rights is to consult an attorney. If you have done steps 3 and 4, it will help the attorney evaluate your rights.
If you cannot afford an attorney, you may be able to find an attorney who give you a reduced fee initial consult using the Wisconsin Bar Lawyer Referral and Information Service at www.legalexplorer.com/lawyer/lawyer.asp