Pumped systems obey a rigid set of fluid flow laws, and from the standpoint of water side designing and balancing, the most important one examines how "pressure drop varies as the square of the flow."

The application and use of this head/flow statement constitutes the basic approach for every complete system and sub-circuit design, pump selection, and therefore, every system balancing situation encountered or ever to be encountered on the water side of a hydronic system, assuming that air problems static pressure problems, and so forth do not exist.