Swimming behind another athlete can save upward of 30 percent energy expenditure. That is, if you’re doing it properly.
Truth: You are wasting time and energy if you are not drafting in the swim leg of a triathlon. There are no rules against drafting another swimmer as long as you do not impede or obstruct their movement. How to make the most of the draft zone:
Get in position
The best and easiest place to draft in open water is directly behind the feet of another swimmer. This position does not cause any interference with the lead swimmer and allows the drafting swimmer to keep track of the leader by following a trail of bubbles. Every time you lift your head to sight the buoys and check your direction, you break neutral body position in the water and lose speed. Following the bubbles of another swimmer allows the drafter to sight less often and save more energy.