Distilled water does not conduct electricity because it does not contain any ionic compounds like acids, bases or salts, dissolved in it. Rainwater, while falling to the earth through the atmosphere, dissolved acidic gases like CO2, SO2, etc. from the air and form acids like carbonic acid (H2CO3) sulphurous acid (H2SO3). etc.These acids provide hydrogen ions (H+) to rainwater. So, due to the presence of these acids, the rainwater conducts electricity.
