Water in Minecraft is textured as Stone slabs in Minecraft snapshot 14w25a. When I exit the world and even the game, I reloaded the world and it seemed to be fine. The textures returned to normal. I'm not sure if this was purposeful, or a huge bug.
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Duplicate of MC-56858 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.
it happened to me too except it was green wool instead