This old building (history undetermined) is located directly on the banks of the Potomac River and adjacent to The C&O Canal, and in modern times houses a raw river water intake facility of the Frederick County (Maryland) Water Treatment System. Apparently this water intake system was installed around 1969 (though the building is much older), and at that time the pollution of the North Branch of the Potomac was so bad nobody would swim or fish in it, much less drink or wash in it. (The fish had all died anyway.) South Branch was OK; I did a lot of swimming and water recreation there. This pumping station is downstream from the confluence of the North Branch and South Branch, and of the Shenandoah River too. I sure hope they used a lot of filters and chlorine back then.