When I had my 4plex I had same problem with nieghbor to my east. My property was just a little higher than hers, She threatened up and down to sue me one time because water drained from my property being higher up than hers when her basement flooded, at that point I had not done any thing that would have forced drain water to her property, the city ords at the time were pretty easy to follow, unless I had made changes to the property that caused water to flow to her lot I was off the hook. SHE on the other hand was still mad as hell about it even though I helped her pump her basement. I felt bad for her , eventually her solution was to dig into her yard, install a french ditch to carry water away and buried it pointing to the home next to hers wich was in foreclosure or condemned , Old home torn down , new one built, New buyer of new home had no idea about the french drain. BUT anyway the point is that if your property sits just a bit lower than the neighbors check with your city/county zoning desk to learn what local ords there may be to address run off. Its possible they might not have any ord OR if they did again it might be like Mpls ord where unless they have done something to change drainage they dont have to do anything, If thats the case your only option may be to learn exactly what your city /county will allow you to do with installing your own drainage system to remove the excess water.
