Essentially, the water rower uses water as it's resistance and the air rower (click here to read our air rowing machine reviews) uses air resistance. Additionally, the resistance of the water gives a very similar feeling to actually rowing in the water. The rowing machines listed above all have fantastic rowing mechanisms that mimic the exact feeling of a rowing a boat.
From a fitness perspective, the WaterRower Natural works 84 percent of your muscle mass, helping tone and strengthen your muscles while burning far more calories than most other aerobic machines. The exercise is also low impact, as it removes all the body weight from the ankles, knees, and hips, but still moves the limbs and joints through a full range of motion--from completely extended to completely contracted.