Back on the trail, we pass a mountain stream. The water sprays over colorful rocks and feeds the flowers alongside the stream. We don’t often think of water as having a color. Most of the time it is transparent and any color we perceive is not due to the water molecule (H2O) but is coming from something in the water (like algae, particulates, etc.). However, there is a subtle mechanism that gives water its blue color under certain circumstances.