Using the National Fire Protection Association standards as a guide, it's unlikely a 4-inch supply bed can provide the apparatus to capacity with hydrant pressure in a forward lay. Any lay more than 100 feet from a hydrant exceeds the hose capacity. If relays supply the fire truck, lays to 350 feet are possible to capacity. The selection of 5-inch hose increases the forward lay lengths to 400 feet and relay lengths to 1,050 feet. Firefighters might incorrectly blame the water system for poor hose performance.
Most complaints result from a lack of water rather than too much water.
Often the hose selected is the reason for supply problems. Often, a department will need a relay valve that can reduce the flow from the hydrant in a forward lay. With a 4-inch hose, a fire truck cannot use its reserve pumping capacity. In most cases, any properly supplied fire engine can double its pump capacity by using the appropriate hose size. That can be critical at large fires in both small and large towns.