This training method is used to gain better chakra control. It involves emitting a constant stream of chakra from the bottom of the one's feet and using the repellent force to walk across the water's surface. This technique is more difficult to master than the Tree Climbing Practice, because the amount of chakra that needs to be emitted changes constantly.
It has also been shown that one can use their chakra to "skate" across the water surface, instead of walking or running. And, as noted by Jiraiya during Episode 14 of Naruto: Shippūden, the more one trains this technique the more they reach a state where they stand on water without even noticing it or basically even trying.
