Bringing a water bottle with you will save you a lot of money and hassle!
If you are a frequent flier then you know how stringent the security checkpoints can be when it comes to liquids. They will confiscate with alarm and disgust your bottle of Poland Springs. Do not fret because I have a solution. The airports have water fountains beyond the check points so one can simply bring an empty water bottle through to fill. This is great since the prices are outlandish in this part of the airport. The use for that water bottle goes beyond just quenching your thirst at the airport.
You may have also noticed that in touristy areas within destinations the prices of water can dramatically be inflated. I once paid 2 euros for a .33 liter bottle of water to then find out the super market a few blocks away was selling 3 liters for 75 cents. Of course I am not going to carry around 3 liters of water but the point is water is something your going to want on your long walks through a destination so you might as well get it at a reasonable price. One tip is you could buy a 2 liter bottle and leave it at your hotel. Then you will have water when you wake up, in the middle of the night, or when you get to the hotel from a long trip. You can also use that larger bottle to fill your smaller bottle that you might take with you. You can feel relieved that you will have water at your hotel when you come stumbling through the door at 2am.
If its a hot destination or cold (be weary as both these environments can catch you by surprise when it comes to dehydration) you want to stay hydrated. You may be able to save some money by bringing that bottle.