A man is sitting in a boat, which is floating in a pond. If the man drink some water from the pond, will the level of water in the pond decrease ?

Explanation

If the man drinks m gram of water from the pond, the weight of (boat + man) system will increase by mg and so the system will displace .m. gram more water for floating. So due to removal of water from pond, the water level in pond will fall but due to water displaced by the floating system the water level in the pond will rise and so the water removed form the pond is equal to the water displaced by the system, the level of water in the pond will remain unchanged.