Neighbour annoyance

Since a week my neighbour has been complaining of water drops occasionally falling from some source inside his house premises. He says it's from my kitchen situated on the 2nd floor and its due to a window net is being cleaned with water. Surprisingly no such cleaning has ever been done at my house. While I am at the office, my 75+ old father and my wife are the only residents at my home. They (my neighbour - a man around 45 and his elderly mother) start complaining at around 2/2:30 pm. Today again they started complaining and called my father and said your daughter-in-law is doing this. Unfortunately for them, I was on leave today and was having lunch at that very moment. I immediately went out and questioned them. They were shocked on seeing me and was not responding initially. When I asked them the source - i.e. the pipe, window, or whatever they believe the water has fallen from, they failed to do so and kept telling where else from would the water fall if not from our house. Incidentally, there are several water pipes just above the place where they claimed water has fallen. I told them to check those pipes but they said those pipes are not faulty. Basically, for any logical question they had no answer. Sometimes they say its because of window net, sometimes they believe its because of some basin washing - basically what they claimed didn't make much sense. But, other neighbours must have thought we (especially my wife) have done some wrong. Now, as I remain at office normally, and if they repeat this thing again, what legal steps can I take? Keeping in mind that a senior citizen and a housewife are only present at home? Thanks.