His glass is half-full—and remains so despite the theatrical little drinky movements he makes. Consider that this is an engineered media moment where the point is to be seen downing that water, not "sipping" it—the most generous possible interpretation of what's going on here with what is a plainly undrunk glass of water.
Here's a screenshot from before he "drinks". The level of the water is just above his grip on the glass:
And here it is after four big gulps:
In the next clip, before it meets his lips:
After a few ostentatious gulps:
All he can do is look suspiciously at the water. Maybe he thinks the glass is cursed.