[syhprum (OP)]

I think the best thing to do would be to jump out clasping hands together if one is sufficiently energetic but I can think of many things not to do!!!

[Bored chemist]

"If a powered on electric heater fell into my plastic bathtub how should I react?"
Surprise- perhaps even shock.
Not getting into the tub is likely to be a good option.

[guest39538]

"If a powered on electric heater fell into my plastic bathtub how should I react?"
Surprise- perhaps even shock.
Not getting into the tub is likely to be a good option.

We should set up that experiment 

[evan_au]

If it is a salt spa, there may be enough current to trip the overcurrent circuit breaker.
- If it is pure water, conductivity is so low that nothing much would happen, provided you kept well away from the heater. The water would boil around the heater element.
- But typical city water is slightly salty, and slightly conductive. Your body fluids are rather salty, and rather conductive, so a fair amount of electricity will flow through you. Not a healthy prospect.

If you tried jumping out, as soon as your foot hit the floor outside the plastic bathtub, the earth leakage circuit breaker should break the current within about 20ms, leaving you shocked but alive.

[syhprum (OP)]

When I suggest jumping out I had in mind both feet leaving the water at once , one foot in the water and one on the wet stone floor might would be palnful but probubly not lethal.
No circait breakers fitted !

[Bored chemist]

Climb up onto the edge of the (plastic, and hence insulating) bath, then step down to the floor.

If the heater is nearer the drain- which may actually be metal, and earthed, than it is to you , there wouldn't be much of a problem anyway. If you are between the heater and the plug you will be in trouble.

If the heater is electrically isolated from ground, there's no real problem until the water gets too hot for you.
The same is true if it's low voltage.
If it's mains powered, and connected via an earth leak trip and the taps are plastic you can try turning the cold tap on full.
With luck the stream of water will carry enough current to earth to trip the circuit breaker.

There's a side order of "sue the builder" here too.

[wolfekeeper]

There's a standard procedure for this: die from electrocution.

IRC Mythbusters did a test on this, they found the current going through your heart was easily enough to kill you. You would have no chance to jump out.