does hot or cold water effect the strenght of a magnet?
The water isn't likely concern, but temperature extremes themself will.
No, but magnetic materials can lose their magnetic property if heated to a high enough temperature known as the Curie point. Below that temperature, you can pick it up with a magnet. Above it, you can't. Too much heat can also destroy a magnet, but these things happen (with common metals) no lower than several hundred degrees F.
