Potassium is also important, whatever mechanism you are losing Sodium (Sweat, urine, diarrhea, vomiting), there's a good chance you're losing Potassium too. Some ORS products also include Zinc because in the developing world it has been shown to reduce the duration and severity of acute and persistent diarrhea. Source: https://www.ncbi.nlm.nih.gov/pubmed/11101480