There may b several factors being responsible for the dryness of mouth, for a few days u take as much water as u can have regularly trying to fulfil atleast 2-3 litres of water intake daily,  if u r a mouth breather thn try to breathe wth ur nose, thre r certain medicines to increase salivary secretion, bt before tht u must go n visit a dentist if the problm still persists,

Elaborate your problem in detail.

Dry mouth can occur due to mouth breathing also. If you are having a nose block or tend to keep your mouth open while sleeping it can cause dry mouth.