The watre which is present in seas and oceans arent fit for drinking. it is because the water contains excess of salt.
desalinating the ocean water and drinking it is done in many countries like saudi arabia, iraq , libya , egypt,etc.
but desalination is very costly. so it is not possible.
when we drink water of seas without desalinating, the excess of salt enters our body and obsorbs all the water in our body by the process called osmosis leading to dehydration.
so , sea water must be desalinated b4 drinking