To realize a long-term use of a swimming pool and to secure domestic water during emergency or disaster by installing in a freely removable manner a sunlight shielding body on swimming pool water, which was not used for a long period of time, thereby preserving water quality sufficient as domestic water.

A sunlight shielding body 2 is installed on pool water surface of a pool body 1 for conserving the water quality for a long period of time. Pool water used for a long time is supplied to a sand layer filtration equipment 3 through a water supply pipe 8 for sending pool water. A pump 4 and an inverter controller 5 are installed on a filtering equipment 3, and the amount of supply water is adjusted and the amount of filtered water is controlled. Then, filtered water is sent to the pool main body 1 through a water supply pipe for sending pool water. During emergency or disaster, filtered water is made ready to supply by switching the valve 14 from the water supply pipe 10 for pool water to the emergency water supply piping 11.