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Water is blue (because water is blue)

By moleculeoftheday on May 27, 2008.

I love stuff like this. A lot of people don't believe that water is blue until they see some really clean water. It really is, though, and the reason is simple yet fascinating. It is because water is blue - very faintly, it's a unique phenomenon because you don't see 10,000 gallon pools of methanol (etc.).

D2O, for example, is not blue.

To see some really brilliantly blue water, take a look at these incredible frozen wave glacier pictures.

Thanks for all the corrections; here is some moving water that does freeze.

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snopes.com did an investigation on that last link. The photos are from Antarctica, not Lake Huron.

The Physics and Chemistry of Color, Kurt Nassau, p. 73. Graph of optical absorption coefficient of water vs. energy. Water has signficant optical absorption from the near-IR through 2.2 eV.

http://www.medphys.ucl.ac.uk/research/borl/homepages/veronica/thesis/ch…
http://omlc.ogi.edu/spectra/water/data/hale73.dat
http://omlc.ogi.edu/spectra/water/data/buiteveld94.dat
http://omlc.ogi.edu/spectra/water/data/warren95.dat
better

Pure water is pale blue.

Along the same lines isn't sky blue, because air is blue

@ thethyme - Water is blue because it absorbs in the red part of the spectrum. The sky is blue during the daytime because of Rayleigh scattering, which is also what causes the sky to be red at the horizon at sunset.
http://en.wikipedia.org/wiki/Rayleigh_scattering

By fullerenedream (not verified) on 27 May 2008 #permalink

Actually, the sky is blue because of a combination of Rayleigh scattering and the weakness of human vision in the blue/violet end of the spectrum. Otherwise, spectrally it should be purple.

my bad I pulled that from an old SGU episode and the only thing I found to back that up is this site
http://www.amasci.com/miscon/miscon4.html#blu

I am not sure if this is accurate or not but I have doubts not finding any additional information to support this position

My emeritus colleague Chuck Braun has a good answer:
"To our knowledge the intrinsic blueness of water is the only example from nature in which color originates from vibrational transitions." (link)

I don't understand how people could not believe water is blue. Have they never seen a picture of the earth from space? Did they then think it was blue because it reflected the sky?

Steve P.: I think people believe that the earth from space is so far outside their experience that radically different things must happen there--for example, if you hold a book at chest height in space and release it, it stays there, which is not known to happen under normal conditions on Earth. Also, most people outside seaside areas will only see large volumes of water in the context of swimming pools, the insides of which are usually painted a light greenish-blue in order to make the water look more inviting. These pool users see the color of the pool walls and mentally "subtract" it from the water's color, and decide it's as clear as the Sprite they're drinking after they swim.

Dear,
According to me the water appear blue is because of the scattering of light.The water that we have seen in photos are mostly in the open space and hence the scattering is prominant. Please see the pure water in dark or take its absorption maxima on Spectroscopy

The sky is blue because the sun is blue. All that scattering stuff is the how not the why -- no blue light to scatter, no blue sky. Though the weakness of human vision in the purple definitely counts as why, too, thanks for that.

This is a pretty old posting, but I hope someone might still respond to my comment/question, which is: there are 4 links to optical absorption data listed above. The first, a thesis, is about near-IR absorption in body tissue water; the last (Warren) is for ice. The other two (Hale & Querry and Buiteveld, Hakvoort, & Donze) disagree TERRIBLY, even though they're supposed to both be for water and reported in the same units. For example, at 350 nm, Hale has 2.33E-3/cm, Buitveld has 9.1E-5/cm. The discrepancies increase from 300 to 350 nm then decrease and flatten to only ~15% difference from 500 to 800 nm. What gives??