Hmm, that's going to need some study - particularly that the article says osmolarity allows for water to flow down the gradient, but then the final paragraph says that water can flow contrary to the gradient too.
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
