You will most likely earn this achievement when you are playing the Hydrocity Zones, which is the 2nd World in a game.
Whilst playing Hydrocity Act 2, you will notice a hand machine which will keep on popping up and down from the ground. If the hand grabs you, it will put you on a speed machine, boosting your speed. This will help you through those swirly slides, and reach the top areas of the level.
As you play along, you will eventually take a hand machine that will make you travel along and then you will go down a water slide, which will lead you to a water pool. With the speed given, you should be able to run across the water, and earn the achievement.
Just keep hold of the
in the direction your going to keep yourself afloat. Don't let go or you'll fall into the water.