Not a composite. Not photoshopped. This is a part of my multiple exposure series.
The Process: I activate the shutter button. This opens the shutter on the camera for a two second period. I keep the shutter button held down which also triggers the drops and the flashes to the intervals I have set on the Time Machine. I hold this button down and the drops keep falling and the flashes keep firing for as many as I can get in before the shutter closes after two seconds. As I am holding down the button, I am also panning the camera on the tripod to hopefully get them all in the frame. It depends on the shape of the drop how many you can fit into the frame and how your panning capabilities are. Quite often they overlap or are slightly out of the frame, so I toss a lot of them.