Before anything else, check whether the discoloration appears in the hot water only or in both hot and cold. This single observation points you in the right direction.

Diagnosing short hot water starts with two questions. First: did it change, or has it always run short? A heater that used to be fine and now runs out points to something developing inside the tank.

The popping, rumbling, or banging that happens when the heater runs is the sound of sediment. Hard water — common across the Phoenix area — carries dissolved minerals like calcium and magnesium that settle out over time and collect as a layer on the bottom of the tank, right over the burner on a gas unit.