Is water a conductor?

We are told to be extra careful about electricity when there is water around. Is water really that good a conductor?

It depends very much on what is in the water. Pure water is a pretty good insulator, but many chemicals can turn it into a conductor. This happens because the chemicals themselves can separate into opposite charges, and then the two charged species can move. For example, dissolving table salt (sodium chloride) in water makes positive sodium ions and negative chloride ions. In one of the activities in this section it is shown that you can get enough current through salty water or vinegary water to make the buzzer buzz or the light emitting diode glow. The current is not very big, but not greatly smaller than the levels that are dangerous (according to the (according to the page about electrical safety). Indeed, an electrical shock is due to electrical current that is flowing through our blood and bodily fluids.

Static electricity

An electrical current moves electrical charge around. However, the wires have equal numbers of positive and negative charges -- they are just moving relative to each other. This is similar to the piping in your house, which always contains the same amount of water, even as it delivers water from the water company to you.

There are situations in which we can have unbalanced electrical charges. Whenever unlike materials are placed in contact, a small amount of charge moves from one to the other. When the materials are separated again, some of this charge "misses the boat" and is left behind. You have witnessed the consequences when you unload the clothes dryer: your wool socks have fallen in love with the polyester T shirt, and a small lightning storm results when you try to separate them. They are stuck together by the separated charges. Because the charges are not moving, they are called static charges.

The amount of charge involved is very small. The amount of charge on the T shirt is the amount that goes through a flashlight bulb in one billionth of a second. However, the charges really really do not like to be separated, and so the voltages involved are actually quite high -- on the order of 10,000 V! The current isn't big, so it isn't particularly dangerous, and indeed the amount of energy involved is small, too.

Static electricity gets to be a nuisance in the winter, when walking across a rug will give you a large enough charge that you get an alarming shock when you touch any large conducting object. The reason it only happens in the winter is that the humidity is low inside. During the summer there is more water in the air, and this gives rise to a thin layer of water on all surfaces. It's just enough to conduct away the static electricity as fast as it is created. Adding a humidifier to your heating system will decrease the static problem, as well as make the air seem warmer.

The section on conductors and resistors