Do the sun's tanning rays penetrate water and to what degree?

All the sun's rays penetrate water, but each color penetrates to a different depth. The colors at the upper end of the light spectrum, especially the UV (ultraviolet) that causes tanning, penetrate deepest. The UV portion of the sun's light can penetrate into clear water for a hundred feet or more at midday. The safest way to avoid overexposure is to remember that if you can see the sunlight, it may cause sunburn, and to limit exposure accordingly or perhaps wear a T-shirt or wet-suit.