The cheapest/lightest alternative to drinking fountain water is a self-contained filter water bottle, which will kill the unpleasant taste/odor of the local water. The version of these made by Brita is very nice, with a wide mouth that can be used to add ice. Unfortunately, Brita has recently discontinued these bottles, but you can still find them on closeout sometimes, and they are often still available through Ebay. It was called the Brita Fill n' Go bottle. We have several, and find them invaluable at theme parks. (We also use them locally at 6 Flags, where they don't allow outside bottled water, but they don't have any objection to an empty bottle.)
Pur also makes a portable filter sports bottle; it's also available through web resources.