This is a sound level indicator, I don't know if it will work, I've made that and at the lowest level it is sensitive, but I don't know if it will be for you, maybe the sound of a drop of water is not very loud for it to detect it, but you can vary the resistors to very low values or maybe you can add another Op. Amp, but that is only a guess 'cause I haven't studied them, i'm sorry it is in spanish, but they areonly a few words.
The LED will lit when the sound level is reached.