Then once you have the best water availed to you make sure you drink enough of it to avoid dehydration. Holding the water a bit longer under the tongue before you swallow apparently helps hydrate our body more than just taking big gulps. Remember that coffee and alcohol dehydrates which is why cafes in Europe traditionally serve a glass of water with the coffee. After a coffee or alcohol replenish with 8ozs glass of water. 

The voice needs to be hydrated there are different opinions about how much water is optimal to drink per day. There is a lot of information on the internet. Most people drink too little but conversely flooding the system is also not good. Try to spread out the amount of water you drink evenly over the day, not all in the evening because you have forgotten to have your quota during the day.