Water and energy billing similarities

There are a lot of similarities between water billing and energy billing. They have the same three inputs - availability (poles and wires, or pipes), capacity (pipe size for water) and usage (measured by a meter). However electricity is generated and either used or lost, whereas water is stored for use on demand. Gas is also stored, but its quality can vary, and a billing application for gas billing must hold the daily variation (known as the calorific factor) in order to discount the gas consumption accordingly.