How would you handle this situation?

[Olivia Aubry]

Hello everyone!

I have quick question for a friend. He is a tenant in a house similar to this one:

(This picture is from Google, not his actual house)

The wall on the right is the beginning of the neighbor's property, no space in between. His problem is that the house floods every time there is heavy rainfall on the right side of the house. He has told his property managers numerous times and they say they can't (or won't) fix it because the problem is on the neighbor's property. What should he do?