Can anyone tell me how to calculate water pressure please; I have water storage tanks running the length of the roof gable (qty 2, 6"dia x 20ft pvc pipe, horizontal, fed by a cystern/ball valve header tank). Can you tell me the water pressure that will give if the tap (3ft from the floor) is 17 feet below the bottom of the storage pipes. Just wondering if using the 17ft head will give enough pressure to a.) fill the washing machine that needs 5psi to open the pressure switch and b.) get enough pressure to have a shower. Will the bore of the pipe from the storage tanks affect the water pressure? Any tips or advice would be greatly appreciated, thanks in advance. Edited to add; this isn't a competition and there are no Blue Peter badges or Crackerjack pencils involved.