I think it can be a great value. Water provides excellent non-weight bearing exercise with some natural resistance. It also provides good cardiovascular exercise as well. Keeping the muscles in tone and the joints moving is the way to go.
Rehabilitation for Arthritis Q & A
There are several issues. The first is whether the pain is coming from your true hip joint or is related to your back or soft tissues such as a trochanteric bursa. The second is whether there contnues to be active inflammation in the hip. Lastly, is there degeneration of the joint. In general, non-weight bearing or low impact exercise is good for joints to maintain muscle tone and range of motion. As always, common sense should prevail.