Forget the cost of water. Ever notice how expensive water bottles are nowadays?
Just to give you an example using relative numbers: In Australia, a bottle of water is around $2.50 to $3.00. A plastic bottle of water from Nalgene, Camelbak, and Sigg + all other manufacturers of aluminium and stainless steel bottles cost between $20-30. I recently went looking for a smaller 400 ml bottle of water to keep in my man-bag (my 900 ml bottle is overly big), and the bottle cost $18.50. It's not like it COMES with water inside it already. It's just plastic. Come on. I remember when Nalgene bottles were $9, and that was for a 1 litre (1000 ml) bottle only 8 years ago.