Electrostatics in the wet!

Question: Explain why simple electrostatic experiments such as picking up bits of paper with an electrified comb never work as well on rainy days as on dry days.

Answer:

Wet air conducts electricity, dry air is a very good insulator. Therefore although you can charge objects up just as well on wet days as on dry ones the charge leaks away through the moist air to the ground really quickly on wet days and so the experiments never work well.

This leakage of charge usually happens so quickly on wet days that the objects never really gain much of a charge at all.