Inspired by Mads Carlsen

Calculus Level 1

Water drips into a cup (shaped like a truncated cone, as below) at a steady rate. The height of the water in the cup

is positive, because it is above the bottom of the cup,
has positive speed, because it is rising, and
has negative acceleration, because the rate at which the water rises is decreasing.

How is the magnitude of acceleration of the water's height changing?