Many water systems have more than one pressure gradient and often times these gradients are supplied with pumps located in the same building. Locally, I can think of one city that has a "Low Service" Hyd. Grad. 1230', "High Service" Hyd. Grad. 1420' and "Super High" Hyd. Grad. 1575. The other gradients, 6 more, are named after the location of the tank serving that gradient.
Steve Wagner