What makes water turquoise?

My mom says it is chlorine.

My HS chemistry teacher said it is the color of the pool/spa/whatever.

I read somewhere that it is the reflection from the (blue) sky. That doesn’t make much sense to me because indoor pools/spa and pools/spas at night are also a turquiose color.

It is the reflection of the sky. Indoor pools are blue because their walls are painted blue.

Just today I was chatting with one of my employers and ended up talking about the last time I flew over the Andes; I told him how there where lakes in some valleys that were of an intense turquoise colour; I suggested that the cause may be high copper content in the water. Could this be so?

You know, I was all set to come in her and say that the ocean in blue for the same reason that the sky is blue, i.e. scattering of white light that ends up being stronger in the blue part of the spectrum. Instead, I find out that it’s due to absorption. And here’s an article from an actual scientific journal to back me up.

Executive summary: water absorbs a small amount of light in the red region of the spectrum, making it appear pale blue (the complimentary colour.) We don’t notice this in a small glass of water, because there’s not enough water for it to work. There’s a picture of a long column of water in my first link, though, which shows a definite blue color.

Oh, and as for the turquoise colour of montane lakes, it’s probably due to small particles in the water.

I don’t think you are talking about water this blue, but some glacier fed lakes are that way due to clay and suspended particles in the water as said above… and also here (scroll 2/3 way down).