These collect rainwater. But the device is designed to collect water even when there is no rain.

VOA: special.2010.07.13

When rain and melting snows flow over a city's streets, parking lots and sidewalks, that runoff picks up all kinds of pollutants residues of petroleum and pesticides, soaps and solvents, as well as pet and wildlife waste.

VOA: standard.2010.08.04