Do not... Do not... Do not do it! My parents bought their house about thirty-five years ago that shared a well and septic system with a very nice old lady next door... Then she had the nerve to die and her children sold the house to some not-so-nice people. The grandfather clause gave them the same shared access to the well and after my father died, it became pure hell! Rather than continue with that aggrevation, my mother had a new well drilled and septic system installed - it's been worth it. Just a thought... Good luck!