I'd say it's probably best to listen to your body and drink water as you needIn the video, there was no mention of water and drinking it, either before, during or after the routine. Is drinking water as needed during the routine/in between steps helpful at least when starting out, and at least for some (all factors - such as environment and physiology - considered), listening to our bodies throughout?
For the BBS exercises, I didn't drink water during a 15 minute routine, and drank after as needed. The same with other exercise done usually. The first morning I did this exercise, I took a break after the Tibetian Rites to drink water.
For the time being, practicing regularly so as to learn the steps and paying attention to posture are what I'm focussing on. I'm curious, as when you're at a gym, there are people drinking water in between steps or routines, and similarly when people go running. Overall, I drink quality water, as good in quality as possible, as needed throughout the day. FWIW.