When an unpolarized light falls on glass, water or any other transparent material, the reflected light is, in general, partially plane polarized. When the light is incident at polarizing angle, the polarization is complete. At this angle, the reflected and transmitted rays are at right angles to each other.
The polarizing angle depends on the refractive index of the material of glass plate on which the (unpolarized) beam of light is incident.
This is known as Brewster’s law. It implies that polarizing angle ip depends on the refractive index of the material.
For air water interface, ip = 53°. It means that when the sun is 37° above the horizontal, the light reflected from a calm pond or lake will be completely linearly polarized.