If you're on desktop and open several videos at once (such as getting home from work/school and opening all the new videos on your subscriptions tab) you really don't notice.
What I do notice are the ads at the beginning, quarters, middle, and end of a video
While this is a cool development I would recommend tempering expectations. The cost of tap water is exceptionally cheap and the claims made here likely take these estimates to the extremes. The economics of scale likely don't match up.
For example, tap water in my city costs ~$0.04 per gallon, at 5 liters per hour, 0.264 gallons per liter, 24 hours per day, for 5 years is $2,312. So saying they can make it for less than the cost of tap water doesn't mean it's affordable.
EDIT: Forgot to convert from liters to gallons