What is Oral Rehydration Solution?
Oral Rehydration Solution (ORS) is a sugar and electrolyte solution used to treat dehydration. It was first developed as a treatment for diarrheal diseases. Having diarrhea can also create a slightly acidic environment in the body which is damaging to your cells. So as well as glucose and electrolytes, ORS contains something called a base which counters the acid. You could rehydrate using intravenous solutions (injecting straight into the blood) but ORS is far easier to work with as you simply drink it! 
Oral Rehydration Solution recipe
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ORS typically contains sodium, potassium, chloride, citrate and glucose. Early ORS had an osmolarity (how concentrated the solution is, or in other words, how many particles there are in a given amount of liquid) the same as in the body. Modern ORS have an osmolarity lower than is found in the body (hypo-osmolar). Having a drink with an osmolarity the same as, or lower than, in the body is important as it ensures that salt and water is absorbed by the intestine. If your drink is too concentrated, your gut will struggle to get the water from it by osmosis.
How does Oral Rehydration Solution work?
ORS works because sodium, and therefore water, absorption in the small intestine is increased by glucose (sugar). The two are carried across the wall of the small intestine together via a mechanism called “the sodium-glucose cotransport mechanism”. The toxins which cause diarrheal diseases, such as from food poisoning, increase secretion of water into the small intestine, but don’t block water uptake by this sodium-glucose transport mechanism. So ORS doesn’t cure you if you’re using it when you have diarrhea, but it will rehydrate you.
When is Oral Rehydration Solution important?
Acute diarrhea is still the second highest cause of mortality in children under the age of 5 in developing countries. ORS is the most feasible form of treatment for this in the field, where the administration of intravenous solutions is impractical. ORS for oral rehydration therapy has been lauded as ‘potentially the most important medical advance of this century’, believed to prevent one to two million deaths per year. Beyond its original clinical application, ORS can also be used to rehydrate after exercising. Some people prefer it to sports drinks as it has a lower sugar content, but the mechanism used to rehydrate is the same.
Hydrant is based on the World Health Organizations standard for ORS, and tweaked for Western lifestyles and diets. Whether you're getting dehydrated through illness, sports or drinking alcohol, it's a great way to quickly replace lost water and electrolytes.
 Gregorio, G et al, Polymer based oral rehydration solutions for treating acute watery diarrhoea, Cochrane Database of Systematic Reviews, 12, 2016 https://www.ncbi.nlm.nih.gov/pubmed/27959472 (A review of data showing that glucose-polymer based ORS for the slow release of glucose and lower osmolarity may be superior to higher osmolarity glucose based ORS)
 Binder, H et al, Oral Rehydration therapy in the second decade of the twenty-first century, Current Gastroenterology Reports, 16:3, 2014 https://www.ncbi.nlm.nih.gov/pubmed/24562469 (A good overview of how and why ORS was originally developed, and continues to be modified)
 Musekiwa, A, Volmink, J, Oral rehydration salt solution for treating cholera: ≤270 mOsm/L solutions vs ≥310 mOsm/L solutions (review), Cochrane Database of Systematic Reviews, 12, 1-44, 2011 https://www.ncbi.nlm.nih.gov/pubmed/22161381 (A review looking at the older iso-osmolar and newer hypo-osmolar ORS formulations and they use for treating cholera)
 WHO, Reports on Individual Drugs, Cholera: can rehydration therapy be improved?, Drug information, 14:2, 14-16, 2000 (How the use of resistance carbohydrates might improved ORS)
 Guerrant, R et al, Cholera, Diarrhea, and Oral Rehydration Therapy: Triumph and Indictment, Clinical Infectious Diseases, 37:3, 398-405, 2003 https://www.ncbi.nlm.nih.gov/pubmed/12884165 (A paper looking at how cholera drove the development of ORT, and how it is being constantly improved)