Rivnuts from Homestead, PA on 6/15/2022 8:52:33 AM:
Water availability along the GAP is somewhat different than along the C&O. There are only two traditional hand pumps along the GAP and only one of those is potable water. However, there are numerous potable water fountains and spigots along the way on the trail itself and places to purchase water within sight of the trail in some locations. The fountains are pretty obvious but some of the spigots may be a little more difficult to spot, especially at night. Also, the GAP passes through several small communities as well where you could politely ask a resident for water if needed.
The longest distances (>15 miles) between available free water would probably be between Whitsett and Connellsville (15 miles), Connellsville and Ohiopyle (17 miles), Confluence and Rockwood (15 miles), Meyersdale and Frostburg (16 miles) and Frostburg and Cumberland (16 miles).
I made a list of available water locations along the GAP. I'll have to find that list or recreate it for your use and others.