1.Surface area of ordinary salt is small. It is very slow to dissolve it, after the salt is stacked.  Top solution of salt container can’t form saturated solution, which influence the regeneration effect of resin.” 

2.Common salt will pollute the surface of reverse osmosis membrane because of its low purity.” 

3.The particles of common salt  is small, so it is risky of jamming the salt absorption tube.” 

4.Common salt is poor of regeneration effect , which severely shorten the service life of reverse osmosis membrane. According to statistics,  the service life of reverse osmosis membraneuse reaches  8 to 10 years in the dialysis center of the European and American countries,  3 to 5 years in the mainland of China. ”