This is a clepsydra — a water clock. For thousands of years, from Egypt to Persia to Han China, people told time by the regulated flow of water through a vessel. Here the idea is rendered as a real, physically simulated glass of water.
The water level is the dial. It rises toward a full glass at the top of each hour and drains steadily down as the minute hand sweeps, so a glance at the level tells you how far through the hour you are. The faint etched marks on the glass are the hour graduations, like the columns scored inside an ancient outflow bowl. The digital readout below mirrors your exact local time.
The water is a single connected body, not a flat rectangle. Its surface is a chain of springy columns that pass waves to their neighbours, so it ripples, sloshes, and settles flat under gravity. The glass refracts and displaces the scene behind it, brightens a meniscus where the water meets the wall, and casts a soft caustic pool of light beneath — the way real glass and water do.
Drag the glass left or right to tilt and pour it; let go and it rights itself and refills to the time. On a phone, tap Motion and physically tilt the device. Pour tips it out, Refill restores it. Tap the glass to cycle the water's tint.