I fell on my knee and now it hurts and now it feels like I have water sensation running down my leg? I have bad sciatic problems and can barely walk.

Have to see doctor. You may have sustained internal injury to knee joint ( ligaments , meniscus etc ) , you have to see orthopedic surgeon for tests and treatment , delay may cause severe damage.
Find a pain medicine. Physician who will examine you, and will make all the necessary treatment recommendations.