Importance of being hydrated at all times

I have realized the benefits of drinking lots of water throughout the day and keeping myself hydrated at all times. I used to drink one liter of water soon after walking up in the morning (after brushing my teeth). This is over and above the water I drink during the course of the day. I used to feel fresher than ever all day. One thing I can say with certainty is that I get lot fewer headaches as a result of keeping myself hydrated.