@ Vijay ..
If it would reduce abdominal fat that means its obviously going to reduce your weight too. Our body weight that we struggle to reduce is made up mainly of water, body fat, bones and muscles. From these all components we can reduce or increase our body fat and muscles. Water is of course a main source of our body to metabolize food, remove toxins, body temperature etc. So its better wedont try reducing water weight but we can reduce the body fat mass by doing kapalbhati pranayam. It would help to reduce your tummy and tone it .