World's Fastest Water Slide: 105 km/h (65mph)

Located in Fortaleza, Brazil, the "Insano" is the highest water slide in the world at 41 meters high, as listed in the Guinness Book of Records. Equivalent in height to a 14-story building, the ride plunges swimmers from sky to pool in just four or five seconds, while traveling at approximately 65 miles an hour. 

The Brazilian water park website describes the Insano as the most extreme equipment of this type of the planet. At the end of the descent the slide levels off and deposits riders safely in a swimming pool to relax.