According to the material it is suppose to be 8km on water and 25km on smooth surface. I have it going pretty good on polish wood floor in the party room and I can see 25km. On water I find that it tend to dive a bit because the fans at the back are pushing it down so I think 8km might be a stretch. I might also be pushing it too hard so maybe less on the throttle in water might actually make it go faster.
Anyway, no reason to doubt either specs. The lift motor is brushless. I have a fully charged 4500mAh last night and ran it for about 5 mins on water and it was down to 80%. The specs claims full speed - 10 mins, 70% for 15 mins and 50% for 20 mins which seems reasonable.
Same controller as my HEMTT so it is a three speed controller.