Military operations in deserts and jungles have a long logistical tail, with supplies for man, vehicle and beast needing to be carried vast distances in hot and difficult conditions. In both cases water is an essential requirement and during the Second World War it soon became apparent that the standard British Army water bottle was not sufficient. What was needed was something with a large capacity that could keep the water pleasantly cool. The British army turned to an ancient East Asian idea they had been using since the early days of the Raj; the Chagul or Chagil. The chagul is a cloth bag that water is put inside. The water slowly evaporates through the fabric, keeping the remaining contents cool. The idea had been used for thousands of years by natives in the far east and the British soon produced canvas bags to take advantage of the principle:
The bag is made of a heavy duty canvas, with a continuous stitched binding along its edge to hold it firmly together and could hold around a gallon of water:
At the spout end a drawstring allows it to be closed off:
Whilst two straps and a loop at the base allow it to be attached to vehicles or carried in a variety of ways:
Instructions printed on the side warn that it needs to be soaked for 48 hours before use to close up the fibres of the bag and make it more watertight:
As can be seen this example dates from 1981, but apart from the date on the outside it is identical to those used during the Second World War. The chagul would retain 85% of its contents over a 24 hour period. Ted Orsborn used them in the desert on the way to Baghdad in 1941:
We packed reserves of fuel in flimsy tin four gallon cans and our water in chaguls, bags made of flax which swells when wet, thus creating a water-tight flask. We tied the latter to the sides of the truck where condensation caused by the passage of air over the surface kept the contents very cool.
Below we see Sepoy Hali Ram of the 19th Indian Division using a chagul for a drink:
This simple design of water carrier was in service with the British Army for many years, apparently they were used during Operation Granby , and examples dated into the 1990s can be found.
Tales from the Supply Depot 
I found two of these in an Army/Navy store that date from 1990. My wife and I hung them from our packs hiking the Grand Canyon. They worked very well in the low humidity keeping our water cool and fresh. They do drip a little, despite a two day soak, and interestingly the tops of the bags not in direct contact with the water dried out!
I think these work better hung on a vehicle or pack animal, but they’re still a cool piece of old school tech that does it’s job. When I spotted a third chagul a year later I snatched it up!