Answer:
Water droplets could obtain charges thru contact with other drops.
Then if two similar drops (both positively charged) came in contact
charge could be transferred because one side of the drop would be positive and one side of the other would be negative by induction.
Several Physics Labs have built experiments called "Kelvins Thunderstorm"
where objects found in the home could be used to build a charge generator that can generate several thousand volts from falling water droplets.
Lightning usually occurs because of the very large potential that can build
because of charge differences between overhead clouds and the induced charge that will then follow in the ground. Mountain climbers know that it's time to look for safer ground when sparks start to jump from the ropes.
