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 reduce environmental impact of plastic bottles from bottled water.
Most airports (especially in the USA) have water fountains located near the restrooms. This is great before an international flight to make sure you have plenty of water to drink on the plane, after you’ve passed security (no liquids or gels above 3 oz or 100ml). However, only place I couldn’t find a water fountain was in Nadi, Fiji. Not sure why there wasn’t one or if there was I couldn’t see it.
Most public parks and shopping centres will have a water fountain. Best water fountain I came across was in Montreal’s Bonsecours Market (in the historic part of town), which has filtered water from their fountain.
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 drinking filtered water through her Bobble. She proudly introduces her Bobble by saying ‘Meet 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. Impressed by the portability and lightness of the product, another friend adores 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!
Enjoy your water & stay hydrated when flying and travelling!