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

VOA: special.2010.07.13

About fifteen centimeters of wet snow has as much water as two and one-half centimeters of rain.

VOA: special.2010.01.05

About seventy-six centimeters of dry snow equals the water in two and one-half centimeters of rain.

VOA: special.2011.01.11

Snow contains much less water than rain.

VOA: special.2010.01.05