Significance of Three Customs Involving String
Chanting and good thoughts of the monks (even any other being) generate positive vibes. The string is used as a better means of conducting the vibration than may be air. (If you attach a tin to the end of two string and you speak into one you can hear the voice in the other.) Generally the string is wrapped around a vessel of water which cases the water to vibrate in tune with the chanting. These strings and water is given out as it the vibrations will carry some positive conditioning.