I had this problem with 2011 car. There is an in-line connector underneath the roof lining close to the tailgate. This connector has a spring and a piston inside so I assume it is meant to act like a non-return valve, but it was actually stopping the water getting to the rear washer nozzle. I took out the spring and the piston and it works fine without it. Beware of trying to blow the line out with high-pressure, or poking through the hose, as there is a risk of dislodging the tubes from the connector, and when you work the washer, it will squirt all over the inside of the roof lining.
Try not to bruise the headlining too much when pulling out the retaining clips.