Decades. It was heavily dependent on your geographic location.

Starting in the late nineteenth centuries cities and fairs were starting to be electrified. Still, in the nineteenth century electric lighting was considered a nice bonus rather than a basic public utility. New York, Detroit, Chicago, and many other cities encouraging private companies to build power stations.

As late as the 1930s, a massive government project called the Tennessee Valley Authority was organized in an effort to get people in that region power and basic infrastructure.

Flash forward - my father-in-law grew up on a farm in the Midwest with no running water or electricity until the late 1950s. Anecdotal evidence, to be sure, but its important to remember that just because some people got power or running water on a certain date doesn't mean all people across the country had access to the same resources.