Seeing it got me thinking about surface tension, the force that gives it the characteristic shape that small drops have.
A simple way to think about surface tension is this: each molecule of water has a certain amount of attractive force between it and its neighbors. However, at the surface, there are no molecules on one side, so the force associated with the other molecules is stronger. Here's a diagram (from Wikipedia):
When a droplet like this sits on a solid surface, it will be spread out slightly by the force of gravity. The height is given by
I'll be leaving for Michigan in a few days to start grad school, so there will be a pause in posting while I move in.