This post on http://www.mytriathlontraining.com/ talks about how it is beneficial to those recovering from injury. Check it out at http://tinyurl.com/ygy4n3a.
The article also outlines how you can engage in the appropriate technique for the maximum benefit from water running.
While this is a good technique, you can try a variety of techniques from what's mentioned here to physically running down the lanes of a pool. Another exercise I've used that's a little fun and different is "towing". Get a partner and wear floating belts around both of your waists. Use a bungee cord to connect your belts from the back and attempt to run away from one another. It's hard to do!