How long should be the gap between water or food intake and Yoga Practice?

You can practice yoga after - 
  (i) 4 hours of eating a heavy meal 
  (ii) 2.5 hours after eating a light meal like fruits/salad.
  (iii) 1.5 hours after drinking a fruit/vegetable juice

You can drink water anytime before the practice. Please avoid drinking water during the practice and right after it. It is best to drink water after a gap of at least 30 minutes.