I just watched Rango, and I got curious of the realistic implications.
Let's set the stage.
Realistic 21st century American tech, unlike the movie.
Some foreign country based on a trade economy.
They're starting to accept foreign trade, but considering that they lack a currency, they settle on using something everyone wants: clean water.
For transaction to be legal, it must be in any size bottle with volume marked, purified (Minerals allowed, as long as they're what you find in common tap water.) and certified sanitary.
Like in Rango, there are banks. They have the expected, a purification center, a test for cleanliness, and a holding tank with UV sanitation system added. Purification is provided for a fee, and required to deposit.
Let's assume they've got easy access to high-quality retail water cleaning machines. I've seen those at camping stores, and they'd sell like hotcakes here because...
...Everyone has to find their own water and clean it. There's a river that one could build a home near, or pipe water from, but tax is higher and there are heavy regulations. Tax is really low away from the river.
City water is a thing, but you have to pay for it with something else. Remember that it's a trade economy, the logic is that they sell stuff to the city and get paid in water.
So, what would this imply? Anything really weird? Could it even hold up?