Electricity is the flow of electrons caused by the attraction of particles with opposite charges and the repulsion of particles with like charges.

In order for electricity to be able to travel through a substance or medium, this difference in charges must be facilitated by the medium.

Electricity runs so well in water because of the large polar characteristic that water has.

The oxygen in the water molecule is very electron-loving meaning that it likes to have more electrons than what it needs. By using the electrons that the hydrogens have, the oxygen carries a partial negative charge. These hydrogens are then electron deficient and carry a partial positive charge. The structure of water, with the partial charges can be found at:
this link.

Notice that there is a large difference in charge between the oxygen and the hydrogens. The large difference gives water a characteristic called polarity which I mentioned earlier. This polarity facilitates the electron movement that makes electricity.

If you drop a hairdryer in the water, the electric current that makes your hair-dryer go can pass though the water because of its polarity. Based on this knowledge, why do you think electricity can pass through the human body?