Earth’s gravity causes water’s surface to curve with the same radius as Earth’s. On glass with a diameter of 10 cm, Earth’s gravity causes the water to form a curvature of 0.00000002 cm, outside other factors like surface tension.
Flat-Earthers like to demand that we prove water curvature in a glass of water. In reality, whatever the container, the curvature of the water surface remains the same as Earth’s radius. On a glass of water, it will be too small to observe.