I understand that the difference in pressure at the inlet and outlet of the RO system indicates that work was done moving the water through the system, but the

I understand that the difference in pressure at the inlet and outlet of the RO system indicates that work was done moving the water through the system, but the RO system is there to fill a glass of water - it's not clear to me why the outlet pressure is relevant. Are you saying that the amount of energy it takes to deliver a given volume of water, varies based on the resistance at the outlet?