Could someone please explain the relationship between water pressure and flow rate. For example, assuming the cold water feed into a house is split and fed in parallel through a 22mm pipe and a 15mm pipe of the same length, what is the relationship between the pipe diameter, pressure and flow rate. Are the following statements correct: The water pressure will be higher in the 15mm pipe as it is of a narrower diameter. The flow rate will be the same in both pipes as that is dependant on the flow rate of the mains cold water supply and isn't affected by the pressure. If a 10 litre bucket was placed under the open end of each pipe, then I assume they would both fill at the same rate, despite one pipe forcing the water out at a higher pressure than the other. As the mains pressure is increased or decreased, the pressure in both pipes would increase or decrease. What would happen to the flow rate? Similarly, if the mains flow rate is increased or decreased, the flow rate in both pipes would increase or decrease. What would happen to the pressure in the pipes? Thanks in advance.