Final answer:
Humans cannot drink sea water because its high salinity creates osmotic pressure that causes dehydration at the cellular level. Desalination can remove salt from seawater, but it requires significant resources. The scarcity and management of fresh water are critical global issues.
Step-by-step explanation:
Why Can't Humans Drink Sea Water?
The simple reason humans cannot drink sea water is due to the osmotic pressure caused by its high salinity. When a person drinks seawater, the osmolarity, which is much higher than that of human bodily fluids, causes water to be drawn out from the cells. This process increases thirst and leads to further dehydration. Unlike some marine animals, humans do not have efficient mechanisms to excrete the excess salt taken in with seawater, and our kidneys cannot cope with such a hypertonic fluid. Drinking seawater ironically leads to cellular dehydration, and can be fatal as it can cause the body's cells to die of thirst.
Desalination is the process by which salt can be removed from water, making it potable. However, it is not a simple task and involves a considerable investment of resources, energy, and technology. Preserving our limited fresh water supplies is thus essential, as only about 1% of Earth's water is accessible for human consumption without desalination.