The only square or rectangular box water tank I have ever seen was on the abandoned (s.g.) line of the DNW&P, a couple miles up the mountain from the east end of the Moffat Tunnel. Did this road have more of this style of tanks? If so, is it known why they favored this box shape? Is it well documented with photos and plans?
I can see the reason for favoring cylindrical tanks. It is the natural shape to contain a mass of liquid that exerts an equal force in all horizontal directions. All the joints are identical and tend to seal simulataneously under the same compressive force as the wood staves expand against the tension of the iron hoop rods.
RK