Your comment about the ATSF water cars jogged my memory.
In a "previous life" I worked for a company that had a potash mine and refinery near Carlsbad, NM. The mine itself was located at Nash Draw - southeast of Carlsbad and about 48 rail miles from the refinery which was due east of Carlsbad.
We had no potable water supply at Nash Draw so Santa Fe provided us with an ancient riveted, full sill tank car that, as I recollect, had a build date from the late '30's. The car was painted silver and stenciled for "Potable Water Only" and something to the effect it was not authorized for use in interline service.
The daily ore shuttle that delivered the raw potash ore to the refinery would bring the empty Santa Fe tank car over one or two days each week. The refinery would load the car with potable water and the next day's shuttle train would pull that along with empty ore cars and deliver everything back to the Nash Draw mine site.
When I look at one of Lionel's "steam era" single dome tank cars, I always think about that ancient, full sill, riveted Santa Fe tank car. 😉