There are numerous videos online of the story and creation of sand mandalas (one of my favorites is available here at CNN, complete with a story, more images and beautiful music). But I like the video below (from 2 years ago) because interspersed with the quick time lapse segments are slow cutaways showing the monks' process of scooping and meticulously placing the sand, as well as some details of how they later destroy the image. (I also like it because it's an original. The poster was also the person who took the video). There is, unfortunately, no footage of placing the sand in the water but I felt that was minor compared to the quality and detail of this video.
Here's the description from the video: "Tibetan Monks painstakingly spend five days to design and place tiny grains of sand to create a beautiful work of temporary art. On day 6 they scoop up the sand and place it in a body of water, releasing the energy of the project back into the community."