Why does the water in the bathtub look blue?

water and light produce. Water is colorless and transparent, but it only allows blue light in light to be refracted, while other colors are directly absorbed. The blue light that penetrates the past hits the bottom of the bathtub and is reflected back, so the water looks blue.

copper ion dissolution copper ion dissolution (if the material inside the water heater or the water pipe is copper), the result of the reaction between copper ion dissolved in water and fatty acid of soap and scale. Usually it only happens in new copper pipes, and it will disappear after a long time of use.