Water towers come in all shapes and sizes.
In a city, tall buildings often need to solve their own water pressure problems. Because the buildings are so tall, they often exceed the height that the city's water pressure can handle. Therefore a tall building will have its own pumps and its own water towers. During a fire, the water demand increases significantly and may greatly exceed the capacity of the pumps at the water plant. A water tower guarantees that there will be enough pressure to keep water flowing through the fire hydrants.