Q: For 21 years, rain runoff from my neighbor’s roof has flowed downhill onto our property in Madison, N.J., where it floods our backyard patio and seeps into our basement, filling our sump pump (which runs most days) and soaking the basement walls, creating mold. The neighbor, a kind older woman, always seemed oblivious to the issue. She recently moved into an assisted-living facility and sold the house to one of her children. I’d like to approach the new owner about the issue, but I’m concerned about alienating the family. What is the best way to go about it?

A: Your neighbor’s runoff seems to be causing, or at least contributing to, your water issues. But for two decades you lived in the house without telling her about it, and she couldn’t fix a problem she didn’t know existed. Neither can the new owners.

“There is no duty to do anything if you don’t know about it,” said Alan S. Golub, a litigator and principal in the New Jersey office of the law firm FSKS.