Don't forget that it was true only for a very small percent of Earth's land/people. For example in Eastern Europe - Bulgaria, electricity reached smaller towns and villages during the 1950s and 60s.
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.