Let’s go back to our basics – we need to understand what Osmosis is. The main piece of equipment required to conduct osmosis is a semi permeable membrane. Does that ring a bell? Of course we have learnt about it in high school - osmosis in plants, osmosis in humans and using the technology in various different applications. 

A semi- permeable membrane is something that allows only one direction of flow through it. A perfect example of it would be our intestines; they allow only the nutrients from the food we eat to get absorbed into our body and the rest doesn’t!

                

Ok, imagine a tub filled with fresh water and a tube containing salty water immersed in it. Of course the end of the tube with the salt water is closed with a semi-permeable membrane. The fresh water moves through the membrane into the salty water trying to bring the salt water and fresh water to the same concentration. 

It is impossible to make the salty water’s concentration to get diluted down to the fresh water levels. Hence when the pressure of the salt water and the fresh water are equal, the osmosis process is complete. This equilibrium pressure is called osmotic pressure.

This is why people can die of dehydration from drinking salty water. When we drink salty water, our body tries to neutralise the salt water and the water in our body by absorbing more and more water. When there is no more water left we get dehydrated and it could be fatal.