Assuming gage pressures in energy calculations

Mass continuity.  (AV) = (AV)

Neglecting minor losses due to bends and fittings in the pipe system

Assuming pipe system is one long pipe for calculating major losses due to friction

For smaller assumptions in energy calculations, see "Energy Analysis" page

For any assumptions in the flow rate calculations, see "Flow Rate Calculations" page

In EGL and HGL, it is assumed that entire pipe system is of constant diameter and is made out of ductile iron 

The temperature of the water in the pipes does not change with respect to time.  This would discount the changes in the temperature of the water due to ambient temperature changes due to seasonal climates.