My ear feels like filled with water, and hurts. There is no actual water though, what can it be and how to get rid of it?

Fluid. While it isn't actually water, it is usually fluid behind the eardrum. The ear has a tube connected to the nose and throat and when you have a lot of sinus drainage, as with allergies or a cold, you can collect fluid behind your ears that makes it feel like your ears are full. Sometimes a decongestant or a prescription nasal spray is necessary but you should see your doctor to be sure.