Fan Casting Water Is Blue in Sort by Tropes

In Real Life, you probably would have misgivings about drinking a glass of some blue substance that presumably is clean water, but in drawn media this is just the way it looks (unless it's unsafe for consumption). It's not just large enough bodies of water to show its inherent blue color (see below); someone might as well have spilled dye into the tap water, and even tears are not exempt. It's just easier to animate it this way, and easier for the audience to see.