Leakage issue

We stay on the 7th floor and the flat on the 6th floor right below us is facing leakage issue. We have not done any changes in both our washrooms. Yet once we helped them repair the leakage problem with our own money. But now again they are facing the same leakage problem. For how long we are supposed to pay for their leakage issue. Also the water pressure in our washroom is very slow and little, which logically can't lead to any leakage problem. Please help with some suggestions.