I thought about asking but I didn't. They did not offer any water time beyond 5 minutes.
5 minutes is actually fine time-wise, unless you've got long hair to wash (?). The shower is smallish and is really only designed for you to get in, wash, and get out.
I am sure they have to load enough water for the number of F passengers, even though most people may pass it up.
As I said earlier, most people were older on both flights (ages in the 50-60 range at least), so maybe they just couldn't be bothered to shower on the plane?