Is water blue because it reflects the sky?

Answer 1

Partially. Large bodies of water do appear blue from relecting blue light from the sky. Consider that the ocean or a large lake does not appear blue on a cloudy day. However, when diving underwater or looking into a pool you may notice a blueish tint. This is due to the water absorbing light at the red end of the spectrum, letting relatively more blue light through. This works when looking though the water, however, rather than simply looking at the surface.

Answer 2

No. The long answer:

The sky is blue because of scattering - when white light encounters the oxygen and nitrogen atoms in the earth's atmosphere, the high frequency section of the white light strikes the orbiting atoms of the nitrogen and oxygen, which causes the high frequency light to be scattered in all directions.

The high frequency light scattered by the molecules in the air are the violet, indigo, and blue colors of white light. These are the colors reflected by the atoms in the atmosphere, and therefore are the colors that we see in the sky.

Transmitted light (from the sun, light bulbs, fire, etc) is made up of a spectrum of colors. The longest wavelengths of light are on the red end of the spectrum and the shortest wavelengths are on the blue/violet end of the spectrum.

When transmitted light such as sunlight enters our atmosphere it collides with the oxygen and nitrogen atoms. The color with the shorter wavelength is scattered more by this collision. Because violet and blue are the shortest wavelengths the sky appears to be violet / blue. But because our eyes are more sensitive to blue light than they are violet light, we perceive the sky as blue.