Question

How is it possible to detect the filling of a bucket under a water tap by hearing the sound standing at a distance?

Answer 1

The pitch of the sound of water filling in a bucket increases as the water in the bucket rises, and the length of the air column decreases.
Thus, the frequency of the sound increases. The sound becomes shriller and shriller as water in the bucket rises.
Hence, by hearing the sound from a distance, one can get an idea of the level of water in the bucket.