My dad has got water on the knee and a cyst and is in intense pain, he has morphine to take and celebrex, (celecoxib) he's scared to take them but should he take ?

He needs evaluation: Has he seen a rheumatologist? Does have gout? The best treatment is to aspirate the knee, evaluate the joint fluid and see what the diagnosis is. He needs a diagnosis to help the pain relief. You can discuss this with your physician.

Evaluation: Simply having "water on the knee" is not always painful. He may have torn or worn cartilage, an infection, a condition called gout, rheumatoid arthritis, etc. Seeing a rheumatologist or an orthopedic surgeon would be the best place to start. Some orthopedic offices have urgent same day or next day appointments.