I keep a 5 gallon water jug with a pump on top that I refill in grocery stores that have RO filtered water dispensers.
In Mexico and Central America there are generic 5 gallon containers that you simply swap out just about in any grocery store. Some countries have different branded 5 gallon containers so you need to pay a deposit and then get your deposit back before you cross the border.
Filtered RO water is pretty cheap, about $0.50 a gallon or less in the US and less than half that in Mexico and Central America.
On my last trip I carried two 5 gallon jugs instead of one.