A friend of mine I met at my hostel in Phnom Penh who does a lot of walking and hitchhiking wants to buy one of those devices that contain water in a special bladder in your pack or attached to it that you drink through a kind of tube hands-free.
Apparently they are known under various names and brand names of which the Camel Pack or Camel Bag type is used by the US army.
The Wikipedia page uses the term "hydration pack". Here's a couple of examples straight from that page.
This is probably very specialized for a developing country so is hard to find and would most likely be in some kind of upmarket outdoors shop used mainly by expats and well-off westernised locals I am assuming.