you can see that the only difference between the diagrams on the left and the diagrams on the right is the resistance in each 'system'. The resistance in the faucet corresponds to the amount that the valve is open. In the wire, the resistance is the size of the opening* in the piece of wire. You can see that the voltage/pressure is the same for both the left and right examples. What you should note in this diagram is... All else being equal, if there is an increase in resistance, the current flow will be reduced. You can see that the current flow in the rightmost wire is half of the current flow in the leftmost wire. This is because the rightmost wire has half of the area for the electrons to pass through.
