How many gallons of water does a city water tank hold on average?

Question

I know a small one holds 50,000.

Answer 1

This really depends on the size of the city that it serves. There are generally requirements for Fire Protection and Drinking Water. Depending on the size of the population they will need to store a certain number of days of drinking water and have a certain amount set aside for fire protection in case of a power failure that shuts down their pumps. See links for some more info.