Does water block uv rays?

Yes, but not very effectively when you are only slightly under the water's surface. As Tim Kaye pointed out, how much UV rays are blocked by water is dependent on the kind and condition of the water. read more

Clear, clean water blocks out little to none of the UV exposed to it. Seawater dos a slightly better job becaus of all the other things in it (like planktons). When UV rays are reflected off of water, they can amplify - causing more damage. Even at a meter deep you will experience the UV rays at ~18% intensity. read more

Like if I'm swimming underwater, will the water protect me from sunburn while I'm underwater (not like deep sea diving, but like swimming). read more