It seems to be useful for outdoor activities such as camping and barbecue. I found a simple and cute water bag at the 300 yen shop "3COINS".
A water bag for easily carrying water. The maximum capacity is 3L, which makes it easy for women to handle. The spout cap was well made and no water leaked from the inside even when tilted. It can be rolled up to make it compact, so it can be easily added to outdoor luggage.
Can hold up to 3L of water,
Can be carried quickly with one hand
Compactly rolled up and stored when not in use
The price is 300 yen each (excluding tax). I think it will be useful as a disaster prevention goods, so why not take it in your hand if you see it at the store?