The true reason why water is blue, is because in reality, water is technically, blue. But how is it that in small quantities, water is depicted as crisp, clean, colorless substance, but in large bodies of water, is observed as blue? What's different between the two? They're both water, right? Yep, they are. Way to go, genius.
"They're both water" - You
The reason that smaller bodies of water appear clear and large bodies of water appear blue, is because water has an intrinsic property, which is caused by absorption and scattering of the the color red. In small amounts, light passes through water relatively easily without changing the 'white light' noticeable to the naked eye. In large amounts, the water absorbs and scatters parts of the white light to create a blue hue of the water. This can be demonstrated by looking at white light through a one meter pipe filled with purified water, closed on both ends with a completely transparent window.
