This video is awesome not just because they built a water slide that lets you do a loop the loop but because it’s a very simple demonstration of the centripetal forces that are in play. You’ll notice that there’s quite a bit of lead up to the actual loop itself, a requirement so that when you start to loop up the sum of the forces ensures that you can overcome the effects of gravity. Too little and you’d only find yourself getting part way around the loop before tumbling down. Too much and you’d risk breaking the supporting structure but you’d have to be going at quite a clip to accomplish that.
If you want to see a good demo of the forces in action the Physics Classroom has a good post on it.