To provide a water bag easily transportable and storable, enabling the easy pouring of water thereinto, tough, suitable for surely preventing immersion from occurring in heavy rain or when rivers are flooded, and suitable for temporarily and surely intercepting rivers when a bank protection work is performed.

Bag parts 2... are continuously joined to each other. Each of the bag parts 2... has a water supply hole h1 at the joining part 2c between the bag parts 2 adjacent to each other. A water pouring hole h2 for pouring water is formed in the bag part 2 of the bag parts 2... positioned at least at one end e2a. When water is poured into the bag part 2 positioned at one end e2a through the water pouring hole h2 of the bag part 2 positioned at one end e2a, water is poured into each of the bag parts 2... continuously joined to each other through the water supply holes h1 formed at the joining part 2c between the bag 2 and the bag 2 adjacent to each other.