Who's regulating amusement, water park rides?

A 10-year-old boy was killed earlier this week on a waterslide in Kansas City. The accident is raising a lot of questions about amusement park safety. As it turns out, there is very little regulation of water slides and roller coasters. Six states have no amusement park regulations at all. So how do you know whether amusement or water park rides are safe enough to ride?