This is one of the tips listed in this article on small things to do to save money:
Save on drinking water
At $1.50 a pop for a gallon of bottled water at the supermarket, the desire
for healthy hydration adds up. By purchasing a water filter, you can cut
your family's water costs to 19¢ a gallon. Order a Brita Riviera pitcher at
amazon.com for $27. Replacement filters good for two months are $9 each.
The trend in bottled water blows my mind. I heard a story on NPR that was saying how bottled water was the new fast growing market for the soda companies, and that since the main buzzword for water is purity, that it was a real challenge for companies to come up with commercials that essentially say:
"Our water has nothing in it but water, but it's still better than the other guy's nothing but water."
Try watching or listening to a bottled water commercial sometime, it's really interesting.
My point is that you should never spend a lot of money on water. I see people at CostCo buying cases and cases of bottled water which I don't understand at all. After all, if you're at home you can drink water from the tap or if you don't like the taste of that you can buy a Brita pitcher and use that. If you're at work, most workplaces have a water cooler or some sort of drinking water available.
This is also a good example of how frugal choices coincide with "green" choices. If you bring a glass or sports bottle to work and fill it from the water cooler it's less wasteful than bringing in, emptying, and disposing of bottle after bottle day after day. Yes it's good if you recycle those empty water bottles but it's even better to not use them in the first place.
The only times I buy bottled water are when I'm on a trip to a part of the world where I can't trust the tap water or I'm at an event (like a ball game) where I want something to drink from the snack bar and don't want soda.