If you do have water on your hip, which can be confirmed by an ultra sound, the treatment is fairly simple. Stop doing whatever activity you are doing that is causing the pain and swelling goes down. Once that is completed you can work on regaining your range of motion, keeping any activity within your pain threshold.
If there is no improvement you will have to seek medical treatment which can include draining the fluid at the joint and possibly getting an injection of a steroid.
Who told you that you have water on your hip and how long have you had it? Was this confirmed with diagnostic imaging (X-rays, MRI, CT, etc.)? What type of doctor are you seeing and what is he/she doing about it? Are you taking any medications or doing any kind of treatment for it?
How did this happen? Were you injured? Does the pain stay in your hip or move to another area?
What makes the pain worse?
What makes the pain better?