Take a reusable water bottle with you wherever you go.
There are usually water fountains around to top it up (not necessarily in developing countries, but sometimes you can boil water or get access to purified water). This will save a lot of money spent on bottled water and also reduce environmental impact of plastic bottles from bottled water.
If you like your purified water, there is a product called Bobble which has a filter at the neck of the bottle. A friend of mine loves her Bobble!
If you want something that is travel light (rolls up uninflated), then there are many new products like Vapur which are an inflatable reusable water bottle. Another friend of mine loves his Vapur type bottle.
My favourite are the Nalgene water bottles, sturdy, BPA free, can handle both hot and cold liquids. Most are all about AUD/USD $10 or less (depends on size).
If you're an american resident, Nalgene are often on sale for $5 at Target!
