Calcium, Carbon, water: Electrical conductivity

For TESTING the electrical conductivity (ELC) of solids and liquids a battery (9 V), a battery clip, a LED (5 V), a pin and a blister with water samples are needed.
Calcium and the carbon of a pencil lead close the electric circle: The LED shows bright light (photo).

Testing the ELC of water samples:

High ELC for salt solutions. 

In order to MEASURE the current passing through water samples a digital multimeter is used.