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... A new study led by Zhongyuan Ni, Rdiger Berger, and Hans-Jrgen Butt at the Max Planck Institute for Polymer Research in Mainz, Germany, has shown that water drops routinely arrive at a surface carrying an electrical charge large enough to punch through an insulating coating. Not scratch it. Not slowly dissolve it. Electrically blow a hole in it, the way a spark jumps a gap.

The starting point of the study is a phenomenon called "slide electrification," which has only been properly quantified in the past few years.

When a water drop slides across an insulating surface like a leaf, a painted wall, a windowpane, or a plastic panel, it strips charge from that surface and leaves an opposing charge behind. The voltages involved are not trivial. Drops charged this way have been measured at up to 9,000 volts. ...

Scientists found that once the coating has been breached, the exposed metal sits in a salty drop with a fresh electrical potential across it. This leaves the ordinary electrochemistry that causes corrosion free to work on the surface it was supposed to be locked out of. ...