Oh, so the force acting on the piston is equal to the force acting on the water? Why is this so, since if I have a 10N force on the water there will be a reaction force of 10N on the piston so won't I have to apply 20N of force rather than 10N so I'm confused about this part.
Thanks for the help guys!
BTW tiny Tim, you seem to be able to pick out the bits that I'm confused about really quickly, that's amazing! Thanks for the help!