can any 1 please tell me whether this is a boat or a plane.

and why in this video are they constantly showing ESC temp read outs.

I think its called a SeaDart.... pretty much something that can do a take off from water like a SeaPlane (http://en.wikipedia.org/wiki/Seaplane)

There are lots of planes that can take off and land in water, and there are already many threads here about such planes.

The readouts are what the owner intended to see via telemetry (again a much discussed topic here, just search).  Ducted fan motors tend to use up lots of power, so people are careful about both battery consumption and how hot the power setup (that is ESC/motor/lipo) gets.  Getting to know the actual values via telemetry is very helpful, especially if they are using a barely adequate power setup.

is the power source on water and in air the same.
i.e. is it a fan if yes then i was not able to spot it.
also, danny i am aware of seaplane but my point here is that external structure of this appears to be of a jet plane and in no way this appears like a sea plane.
just have a look at the extremely streamlined front area. similar to a jet

Fans ?  Those are ducted fan motors, as I mentioned in the earlier post. 

Any thing/plane that can float and gather speed on water can take off without getting water into into electrics/electronics will work fine.  The shape does not really matter. Usually one would put "floats" on the landing skids of planes to make them land/take-off from water, in this case he has attached something similar to "floats" along the underbelly.