To provide a domestic waste water treating method giving no excessive water amt. load and org. matter load to a septic tank for sewage, stable in the quality of treated water and without generating a problem such as a malodor.

In the case that waste waters discharged from a toilet 3, a kitchen 4 and a bath room.lavatory.laundry 2 are made to stay respectively in waste water pits 7, 8 and 5 and the all or a part of the waste waters are purified and treated at the septic tank, the waste water discharged from the toilet 3 and the kitchen 4 are introduced to the septic tank 9 and treated there, the waste water discharged from the bath room.lavatory.laundry 2 is introduced to the septic tank 9 and treated there when an indicated value by a suspended material detecting sensor 14 provided at the waste water pit 5 for the both room.lavatory.laundry 2 is more than a prescribed value and the domestic waste waters are introduced to a storage tank 10 (are not introduced to the septic tank) and treated when the indicated value is less than the prescribed value.