Even seemingly modern, developed countries didn't have indoor plumbing in the 1930s.

My parents grew up in houses on modern (for the time) housing estates in England in the 1950s/1960s without indoor plumbing. Though it was indoor in the sense that the shed was attached to the house out back, but the plumbing was not inside the house until the late 1960s.

The number of dwellings in Japan with flush toilets increased from 45.9% in 1978 to 83.0% in 1998.

* Statistics Bureau, Japan.