Submerging the glass in water is simply an easy way to keep the drill bit lubricated with water. You could also apply a constant trickle of fresh water to the drill bit, if the glass couldn't be submerged. The idea is to flush the little bits of glass away, as they break off, and to keep the drill bit from getting too hot.
Acrobatic_Wonder8996 t1_izxj04w wrote
Reply to How does putting glass underwater, prevent it from breaking when drilling/cutting? by emelrad12
Submerging the glass in water is simply an easy way to keep the drill bit lubricated with water. You could also apply a constant trickle of fresh water to the drill bit, if the glass couldn't be submerged. The idea is to flush the little bits of glass away, as they break off, and to keep the drill bit from getting too hot.