Salt in the human body make us live by activating our brain cells , for good digestion etc. Actually the quantity of salt one should consume in a day is hardly 100mg which we obviously get from the daily meals i.e from the raw vegetables, fruits, grains and pulses.
We all know that our body is made up of millions of cells. When the intake of salt grows the salt is accumulated on inside and outside the cell. This is similar to a toxic waste. If we drink water more there is a great chance of the salt to drag away from the cell. Hence our sweat is salty.