First take a live photo of running water
On an iPhone, open the camera and make sure the “Live Photo” button is on. It’s the bullseye circles in the upper left corner. Tap it to see “Live On.” Now take a photo of some running water. When you view that photo, using Apple photos, you can long press and see the movement of the water. To make the soft waterfall effect, just swipe up on the photo and then choose “Long Exposure.” Watch the video below to see exactly how to do it.