Of the glasses at the bottom, 5 will fill up first. It is possible for #1 to fill up first if the volume of water pouring into it is greater than the volume leaving it through the tube.
I just saw that there is a line on the spigot to the left of 1... I guess no water will flow. Only 3 and 5 will get water to them. So only 5 will fill. I was so busy figuring the lowest one, I did not notice some are open some are a line. my bad.
