what is the most common source of dissolved solids in sea water
Salt is, of course, the most common substance found in sea water, but it is far from being the only one. In fact, sea water is actually quite rich in mineral solids. The solids dissolved in sea water vary from about 1 per cent where rivers enter the sea to about 4 per cent where the circulation of water is partly restricted, but they average about 3.5 per cent (one hundred pounds of sea water, if boiled away, will leave behind close to 3.5 pounds of solids). Most of this is ordinary salt -- sodium choloride.