OK John,
At 7.5" that scales in 1:29 to roughly 18’ diameter. (7.5X2/12=18) I cheat because I am no geometry major and us an online calculator to figure out that the volume of an 9’ radius sphere is 3050 cubic feet which is 23,790 gallons (3050 X 7.48=23,790). Now at 35" that scales out to 85’ to top of tank. At 85’ the pressure at ground level would be a whopping 36.5psi. 25,000 gallons could very easy serve a rail yard, small non water intensive industry, or small rural farm community of maybe 200-300 connections. The pressure is what would be the real world killer.
Realistically that is a small tank and very anemic water pressure. But here is the thing, who cares. Does it look good, yes. I like the overall proportions. I would go with it for sure. No one is going to sit down and do the math. One real world scenario would to put that exact structure on a grassy knoll behind a wall. . .oh wait that is a secret government sniper position. But placing this on a hill even a small one would be a real world solution. Something else to consider and could help give forced perspective is that often water tanks are located away from town based on said hill or its location in relation to the water source. Our 50,000 gallon reservoir was located about 1/2 a mile away from its first connection because that was about half way to the lake that fed it. These are just some ideas of what real world people do to solve the hydraulics problem. To further add to the plausibility of this idea is that often when reservoirs can’t be tall for what ever reason (airport vicinity, or an area that serves multiple elevations where the bottom elevation can’t be over pressurized) then a low tank would be used in conjunction pressure tanks and pumps to boost pressure.
