To provide a reasonable constitutive technique for obtaining intermediate water by treating waste water and using the obtained intermediate water as toilet washing water.

The subject system for treating the intermediate water has an intermediate water treatment tank 101 for treating the water to be treated to obtain the intermediate water, a toilet 105 having a water feeding tank 106, an intermediate water supplying route 102 for supplying the intermediate water from the tank 101 to the tank 106, a clean water supplying route 107 for supplying cleane water to the tank 106 and a clean water supply amount adjusting means 108. The amount of the clean water to be supplied to the tank 106 can be adjusted by the means 108 according to the amount of the intermediate water to be supplied to the tank 106 through the route 102.