Hot water is not actually heavier than cold water. In fact, water behaves somewhat counterintuitively when it comes to temperature and density.
As water is heated, its molecules gain energy and move more vigorously, causing them to spread out and become less dense. This decrease in density is primarily due to the expansion of water molecules when they are heated. Therefore, hot water is actually less dense than cold water.
The reason hot water sometimes appears to be "heavier" is because hot water molecules tend to rise, creating convection currents. When you pour hot water into a container of cold water, the hotter water rises to the top due to its lower density, while the cooler water sinks to the bottom. This mixing of hot and cold water can create the impression that hot water is heavier, but it is simply a result of the different densities and the resulting convection.
It's worth noting that the difference in density between hot and cold water is relatively small and may not be easily noticeable in everyday situations.