This is a very secure loop probably developed for use in an environment that make security properties for most knots change dramatically... underwater. Although shown separated for clarity, draw the two half-hitches snug together before using.
Some theorize that its form also prevents jamming in wet line.
If you're going to use it, please don't tie it the landlubber's way! Learn to form the signature bowline loops (half-hitches) by twisting the end of the line over, under and upward around the standing part, in one quick motion to force the half hitch to form in the standing part.. Practice this with a simple bowline before moving on to the water bowline. Not only is this a quicker method, it also greatly reduces the odds of you tying the knot incorrectly.