Why is water as a gas white but as a liquid transparent? I understood that clouds are white due to the size of the molecules - therefore liquid water should have the same color because the molecules will not grow.

Question

anonymous · Answer

You are almost right.  It is not because of the size of the molecules, but the size of the water droplets that make them up.  The size of the water droplets are the right size to scatter all wavelengths of visible light, and hence they appear white.  Liquid water appears transparent because the body of water is just too large to cause this scattering.

anonymous · Answer

What do you mean with "body of water"? A cup of water does not have a smaller body than a large cloud in the sky?

anonymous · Answer

Sorry, I mean with respect to the size of the water drops taht make up teh cloud and the cup of water.    

A cloud is an object made of very small water drops, where the drops are separated by air, (and hence the density of the overall cloud is not much greater than that of the air comparatively speaking).  A cup of water can be thought of as one large water drop of liquid.  

A cloud of water droplets will scatter more light than a cup of water, even though they may contain the same volume of water.

anonymous · Answer

thx - now I understand your point - problem solved :)