The sea water is heavier than the river water and river water is heavier than the rain water.
Because, which water has many minerals, that water has heavy weight. But the rain water does not have many minerals. It has less minerals. That is why it has light weight.
The source of water is rain. Because of raining, the rivers, the ponds, and the lakes are filled with the water.
In sunlight, the water molecules are evaporated. But which water molecules have many minerals are left. There are salts besides the minerals. The evaporated water forms clouds so the rain water has light weight. When the raining, the water flows in the rivers. The rivers flow is through the different types of soil. The minerals are mixed in the water which are in the soil. Again this water has heavy water. This is about light weight of the water.
Article by: Sri