Short answer: WHO/UNICEF reduced-osmolarity oral rehydration solution (ORS) has a total osmolarity of 245 mOsm/L. It contains 75 mmol/L sodium and 75 mmol/L glucose, a 1:1 ratio that drives sodium–glucose co-transport in the gut [1, 2]. Sports drinks, juices and sodas are a different kind of product. Published measurements put a typical sports drink at about 330 mOsm/kg and apple juice at about 700–730, with only a small fraction of ORS’s sodium [3, 4, 5]. MSD’s pediatric chapter says these drinks “do not meet these criteria and should not be used” for oral rehydration: they carry too little sodium and too much carbohydrate, and the osmotic effect of the excess carbohydrate “may result in additional fluid loss” [6]. MSD’s consumer guide says the same: sports drinks, sodas and juices “have too little sodium and too much carbohydrate and should not be used” [10].
Units on this page. Formulation documents give osmolarity (mOsm/L, calculated). Laboratory studies of drinks report measured osmolality (mOsm/kg, equivalent to mmol/kg). At these concentrations the two are close but not identical. We label each value with the unit its source used. See Osmolality vs Osmolarity.
1. WHO reduced-osmolarity ORS: composition
WHO/UNICEF recommend this formulation in place of the earlier 311 mOsm/L ORS [1, 2]:
| Ingredient | g per liter | Component | mmol/L | |
|---|---|---|---|---|
| Sodium chloride | 2.6 | Sodium | 75 | |
| Glucose, anhydrous | 13.5 | Chloride | 65 | |
| Potassium chloride | 1.5 | Glucose, anhydrous | 75 | |
| Trisodium citrate, dihydrate | 2.9 | Potassium | 20 | |
| Total | 20.5 | Citrate | 10 | |
| Total osmolarity | 245 |
UNICEF’s product specification for the 20.5 g sachet allows ±10% on each electrolyte and on glucose [7].
Why the osmolarity was lowered
The original WHO ORS was 311 mOsm/L, with sodium 90 and glucose 111 mmol/L [2, 3]. Trials of reduced-osmolarity ORS in children with acute non-cholera diarrhea showed the following [1, 2]:
- the need for unscheduled IV therapy fell by 33%;
- in pooled studies of reduced-osmolarity solutions (210–268 mOsm/L, sodium 50–75 mEq/L), stool output fell by about 20% and vomiting by about 30%.
In adults with cholera, WHO notes the reduced-osmolarity ORS is as effective as the standard ORS but is associated with more transient, asymptomatic hyponatremia [2].
The physiological basis: water follows solute. Luminal-perfusion work in healthy volunteers, as summarized by Sollanek et al. [8], found the fastest net fluid absorption with hypotonic drinks of about 200–260 mmol/kg [8]. Sollanek et al. used that same range as the compliance window when they tested commercial products [8].
2. Published osmolality data: ORS, sports drinks, juice, soda
These are values from the cited publications, not current label claims. Products are reformulated, so treat them as historical data points.
Measured in 2019 (freezing-point osmometry; Sollanek et al.) [8]
| Product (as tested) | Measured osmolality (mmol/kg) | Within 200–260? |
|---|---|---|
| enterade (amino-acid ORS) | ~211 | Yes |
| Pedialyte Classic (pre-mixed) | ~313 | No |
| Gatorade (orange) | ~334 | No |
| Speedlyte | ~406 | No |
| 5 of 6 powdered ORS (Hydralyte, CeraLyte 70, Dioralyte, DripDrop, TRIORAL) | within range | Yes |
| Dioralyte Relief (rice-based powder) | ~145 | No (low) |
Two further findings from the same study [8]:
- Gatorade’s osmolality rose by about 108 mmol/kg after 60 days stored at about 31 °C (sucrose hydrolysis splits one particle into two).
- Conflict of interest: the study was funded by the maker of enterade, and two authors were paid consultants to it [8].
Older reference tables (pediatric guidelines and reviews)
| Drink | Osmolality / osmolarity | Sodium | Source |
|---|---|---|---|
| Apple juice | 730 mOsm/L | 0.4 mmol/L | CDC MMWR 2003 [3] |
| Coca-Cola Classic | 650 mOsm/L | 1.6 mmol/L | CDC MMWR 2003 [3] |
| Cola | 550 mOsm/kg | 2 mEq/L | AFP 1999 [4] |
| Ginger ale | 540 mOsm/kg | 3 mEq/L | AFP 1999 [4] |
| Apple juice | 700 mOsm/kg | 3 mEq/L | AFP 1999 [4] |
| Gatorade | 330 mOsm/kg | 20 mEq/L | AFP 1999 [4] |
| Chicken broth | 450 mOsm/kg | 250 mEq/L | AFP 1999 [4] |
| Tea | 5 mOsm/kg | 0 | AFP 1999 [4] |
| Orange juice | 587 mOsm/kg | 1.0 mmol/L | ESPGHAN 2001 [5] |
| Apple juice | 694 mOsm/kg | 0.0 mmol/L | ESPGHAN 2001 [5] |
| Coca-Cola / Pepsi | 469 / 576 mOsm/kg | 3.0 / 1.0 mmol/L | ESPGHAN 2001 [5] |
Commercial ORS in the same CDC table (2003 formulations): Pedialyte 250, Enfalyte 200, CeraLyte 220, Rehydralyte 305 mOsm/L [3] (2003 formulations; current products differ).
Values for the same kind of drink vary between sources (apple juice 694–730; cola 469–650) because of brand, formulation and method. The direction is consistent, though: juices and sodas are roughly 1.5–2.5× plasma osmolality and contain almost no sodium.
3. Why hyperosmolar drinks can worsen diarrhea
- Osmotic water pull. Sugar that is not absorbed fast enough stays in the gut lumen as an osmotically active solute. Water follows it into the lumen, adding to stool water. This is the same mechanism as osmotic diarrhea. AFP calls it “osmotic worsening of diarrhea” [4], and MSD notes that excess carbohydrate “may result in additional fluid loss” [6].
- Wrong sodium-to-glucose ratio. Sodium–glucose co-transport works best at a 1:1 ratio, which is what WHO ORS provides (75:75) [6]. Sports drinks and juices carry far more carbohydrate than sodium [3, 4, 6].
- Too little sodium. Low-sodium fluids replace water without replacing sodium. AFP notes that this may contribute to hyponatremia [4]. (The reverse problem: chicken broth’s very high sodium makes it unsuitable [4].)
- It’s not only osmolality. Some commercial “ORS” products have measured osmolalities above the old WHO formula’s 311 mOsm/L (calculated) [8]. The label word “electrolyte” does not guarantee a WHO-compliant composition.
WHO draws “a clear distinction” between products for treating or preventing dehydration from diarrhea and preparations “designed for replacing water and salt losses during exercise (sport drinks)”. It asks sports-drink makers not to promote them for diarrhea [2].
4. Worked examples
Example 1: Add up WHO ORS osmolarity
Step 1. List the particles (mmol/L) [1]. Na⁺ 75, Cl⁻ 65, K⁺ 20, citrate 10, glucose 75. Step 2. Sum. 75 + 65 + 20 + 10 + 75 = 245 mOsm/L. Step 3. Compare with plasma. Plasma osmolality is about 275–295 mOsm/kg [9], so the solution is hypo-osmolar, by design.
Example 2: Reproduce the mmol/L values from the grams
| Salt (g/L) | Molar mass (g/mol) | mmol/L | Particles contributed |
|---|---|---|---|
| NaCl 2.6 | 58.44 | 2.6 ÷ 58.44 = 44.5 | Na⁺ 44.5, Cl⁻ 44.5 |
| KCl 1.5 | 74.55 | 1.5 ÷ 74.55 = 20.1 | K⁺ 20.1, Cl⁻ 20.1 |
| Trisodium citrate·2H₂O 2.9 | 294.10 | 2.9 ÷ 294.10 = 9.86 | Na⁺ 3 × 9.86 = 29.6, citrate 9.86 |
| Glucose (anhydrous) 13.5 | 180.16 | 13.5 ÷ 180.16 = 74.9 | glucose 74.9 |
Totals: Na⁺ 44.5 + 29.6 = 74.1. Cl⁻ 44.5 + 20.1 = 64.6. K⁺ 20.1. Citrate 9.9. Glucose 74.9. Sum: 74.1 + 64.6 + 20.1 + 9.9 + 74.9 = 243.6 ≈ 245 mOsm/L. The published values are rounded [1].
Example 3: How far is a sports drink from ORS?
Measured Gatorade ≈ 334 mmol/kg [8]. WHO ORS = 245 [1].
Units caveat: 334 is a measured osmolality (mmol/kg); 245 is WHO’s calculated osmolarity (mOsm/L). At these concentrations the two are close, so the comparison is approximate. (Sollanek et al. made the same approximation, treating WHO ORS as 245 mmol/kg [8].)
Step 1. Difference. 334 − 245 ≈ 89 higher (approximate, mixed units). Step 2. Ratio. 334 ÷ 245 = 1.36× the ORS value. Step 3. Against the absorption window. 334 is above the 200–260 mmol/kg range associated with the fastest net fluid absorption [8]. Step 4. Sodium. About 20 mEq/L [4] vs 75 mmol/L in WHO ORS [1], roughly 27% of the ORS sodium.
Example 4: Why “watered-down juice” still isn’t ORS (ideal-dilution arithmetic)
Apple juice per CDC: 730 mOsm/L, sodium 0.4 mmol/L [3]. Suppose it is diluted 1:1 with water. Assume ideal behavior and ignore the water’s own minerals.
Step 1. Osmolarity. 730 ÷ 2 = 365 mOsm/L, still above WHO ORS (245) and above plasma. Step 2. Sodium. 0.4 ÷ 2 = 0.2 mmol/L, vs 75 in ORS. Step 3. Conclusion. Diluting juice lowers its osmolarity, but it does not create a sodium–glucose rehydration solution. This is an arithmetic illustration, not a recipe.
5. Practice questions
Q1. What are the sodium and glucose concentrations and the total osmolarity of WHO reduced-osmolarity ORS?
Answer
Sodium 75 mmol/L, glucose 75 mmol/L, total 245 mOsm/L [1, 2]. The 1:1 sodium:glucose ratio supports sodium–glucose co-transport [6].
Q2. WHO lowered ORS osmolarity from 311 to 245 mOsm/L. Name two outcomes that improved in children with non-cholera diarrhea.
Answer
Unscheduled IV therapy fell by 33%. In pooled studies, stool output fell by about 20% and vomiting by about 30% [1, 2].
Q3. Why can apple juice worsen diarrhea even though it “contains fluid”?
Answer
Its osmolality is about 700–730 [3, 4], with lots of carbohydrate and almost no sodium. Unabsorbed sugar holds water in the gut lumen (osmotic effect), adding to stool losses [4, 6], and the low sodium does not replace sodium losses.
Q4. A pre-mixed “electrolyte solution” measured 406 mmol/kg in a lab study. Is it within the 200–260 mmol/kg window? What does that tell you about labels?
Answer
No. It is well above the window, and above the old WHO formula’s calculated 311 mOsm/L [8]. Osmolality is not required on nutrition labels, and some products marketed for rehydration do not meet WHO osmolality targets. Independent measurement matters [8].
Q5. Calculate the osmolarity contribution of the glucose in WHO ORS from its mass.
Answer
13.5 g/L ÷ 180.16 g/mol = 0.0749 mol/L = 74.9 mOsm/L (≈ 75) [1]. Glucose does not dissociate, so 1 mmol = 1 mOsm.
When to see a doctor
Based on MSD Manual guidance for children with diarrhea [10]. Get medical care right away if there are:
- signs of dehydration: peeing much less, unusual sleepiness or listlessness, crying without tears, extreme thirst, dry mouth, or weight loss;
- an ill appearance, high fever, or blood in the stool;
- severe belly pain or marked tenderness;
- tiny reddish-purple spots or bruise-like patches on the skin;
- a child who is not drinking, or drinking very little.
Even without warning signs, call a doctor if diarrhea lasts 2 days or more or there are more than 6–8 episodes a day [10]. Infants and young children can become dehydrated quickly, sometimes in less than a day [10].
MSD also notes: “Medications to stop diarrhea, such as loperamide, are not recommended for infants and young children” [10].
Our advice for babies and infants: do not make home-made rehydration drinks, and do not choose or dose rehydration fluids for an infant on your own. Ask a doctor, nurse or pharmacist which product to use and how much.
Related tools and pages
- Osmolality vs Osmolarity
- Isotonic, Hypotonic, Hypertonic
- Enteral Formula Osmolality
- Normal Osmolality Range
- Disclaimer
Educational content, not medical advice. This page compares published composition data. It does not tell you how to treat dehydration or diarrhea, and it is not a recipe. Product data are historical and may not reflect current formulations. For infants, children, older adults, pregnancy, or anyone with kidney, heart or other chronic conditions, ask a clinician before choosing a rehydration product.
References
- WHO/UNICEF. Joint Statement: Clinical Management of Acute Diarrhoea. 2004. https://iris.who.int/server/api/core/bitstreams/8545a008-43cf-4ea2-927e-2d4664fd7938/content
- WHO. Oral Rehydration Salts: Production of the new ORS. WHO/FCH/CAH/06.1. 2006. https://iris.who.int/server/api/core/bitstreams/e52f1746-cf33-4a63-9f97-4c0bfaaeb230/content
- King CK, Glass R, Bresee JS, Duggan C. Managing acute gastroenteritis among children: oral rehydration, maintenance, and nutritional therapy. MMWR Recomm Rep. 2003;52(RR-16):1–16 (Table 3). https://www.cdc.gov/mmwr/pdf/rr/rr5216.pdf (mirror: https://stacks.cdc.gov/view/cdc/13471/cdc_13471_DS1.pdf)
- Burkhart DM. Management of Acute Gastroenteritis in Children. Am Fam Physician. 1999;60(9):2555–2563 (Table 7). https://www.aafp.org/afp/1999/1201/p2555
- Sandhu BK; ESPGHAN Working Group on Acute Diarrhoea. Practical guidelines for the management of gastroenteritis in children. J Pediatr Gastroenterol Nutr. 2001;33 Suppl 2:S36–S39. https://doi.org/10.1002/j.1536-4801.2001.tb07524.x
- Cellucci MF. Oral Rehydration Therapy. MSD Manual Professional Version (reviewed Jan 2025). https://www.msdmanuals.com/professional/pediatrics/dehydration-and-fluid-therapy-in-children/oral-rehydration-therapy
- UNICEF Supply Catalogue. ORS low osm. 20.5 g/1 L, pack of 10 (S1561133). https://supply.unicef.org/s1561133.html
- Sollanek KJ, Kenefick RW, Cheuvront SN. Osmolality of Commercially Available Oral Rehydration Solutions: Impact of Brand, Storage Time, and Temperature. Nutrients. 2019;11(7):1485. https://pmc.ncbi.nlm.nih.gov/articles/PMC6682936/
- StatPearls. Serum Osmolality. NCBI Bookshelf NBK567764. https://www.ncbi.nlm.nih.gov/books/NBK567764/
- Consolini DM. Diarrhea in Children. MSD Manual Consumer Version (reviewed Mar 2025). https://www.msdmanuals.com/home/children-s-health-issues/symptoms-in-infants-and-children/diarrhea-in-children