The top speed of a Jet Ski depends on the type of Jet Ski and the size of the Jet Ski but most Jet Skis have a top speed of 55 MPH.
Most Jet Skis and go from 0 MPH to 55 MPH in as little as 2.9 seconds which is pretty fast.
There are however some models of Jet Skis that can reach higher speeds such as the Seadoo RXP model Jet Ski that can reach 70 MPH as a top speed.