The 3 or 4 CP water tanks I have seen over the past 50 years on the prairies
were all steel tanks built atop of a steel structure but enclosed in a wooden
shell so it could be heated in winter. I remember as a youngster the water tank
at Weyburn, SK coming down in the late 50s. I thought it would have been all
wood but when the exterior shell was taken down there was the steel tank inside.
Most of the wooden shells had straight perpendicular walls but some had walls
slanted from the bottom up about half way.
Midhurst was also a steel tank with a heater installed in the
base. I don't believe any steel tank was enclosed.