When should I use Hydralyte or Gastrolyte rather than just water?

Use Hydralyte, Gastrolyte, or any oral rehydration solution when you have active gastroenteritis with diarrhoea or vomiting, when you are sweating heavily in heat for more than 90–120 minutes, or during endurance exercise beyond that threshold. For everyday drinking, mild exercise under an hour, or ordinary hot-weather exposure with a normal diet, plain water is adequate. Signs of meaningful dehydration that warrant ORS include dark urine, no urine for eight hours, dry mouth, dizziness on standing, or feeling faint — these also warrant a GP review if not improving.

What is in WHO oral rehydration solution and why does it work better than water?

WHO reduced-osmolarity ORS contains sodium 75 mmol/L, glucose 75 mmol/L, potassium 20 mmol/L, chloride 65 mmol/L, and citrate 10 mmol/L, at an osmolarity of 245 mOsm/L. It works because the intestinal sodium-glucose co-transporter SGLT1 binds one sodium and one glucose simultaneously, transporting both into the gut wall with water following the osmotic gradient. This mechanism is preserved during diarrhoeal illness when other sodium-transport pathways fail, making ORS significantly more effective than plain water. Australian Hydralyte and Gastrolyte use a slightly lower-sodium variant to improve palatability for children while retaining the same SGLT1 principle.

Can I drink too much water during exercise?

Yes — overdrinking plain water during endurance events is a documented risk. The condition is called exercise-associated hyponatraemia: when sodium falls due to excessive plain-water intake, fluid shifts into brain cells, causing headache, confusion, seizure, and in severe cases death. A 2005 NEJM study found 13% of Boston Marathon finishers had hyponatraemia after the race, primarily from drinking too much rather than too little. Current consensus is to drink to thirst. If exercising beyond 90 minutes in heat, use a fluid providing 30–50 mmol sodium per litre rather than plain water.

Should I use daily electrolyte drinks like LMNT or Liquid IV?

For most healthy Australian adults, there is no clinical need for daily high-sodium wellness electrolytes. The average Australian diet already exceeds the sodium Adequate Intake, so adding a daily serving of LMNT (approximately 1 g sodium) or Liquid IV (approximately 500 mg sodium) adds unnecessary sodium load. These products serve a genuine niche in specific situations — ketogenic-diet adaptation, ultra-endurance athletes, people with confirmed high sweat-sodium, post-bariatric surgery, post-illness recovery, or prolonged occupational heat exposure — but routine daily use in an otherwise healthy adult is not clinically justified and is contraindicated in hypertension, chronic kidney disease, and chronic heart failure.

What are the signs of heat stroke and what should I do?

Exertional heat stroke is a medical emergency requiring immediate action. Warning signs are core body temperature at or above 40°C combined with central nervous system dysfunction — confusion, slurred speech, unsteady gait, collapse, or seizure. Call 000 immediately and begin cold-water immersion (neck-down in cold or iced water) while waiting for the ambulance. Cooling before transport is the clinical priority — delay increases mortality. Less severe heat illness includes heat exhaustion (temperature 38–40°C, headache, nausea, sweating, mildly confused) and heat cramps — treated by stopping activity, moving to shade, and giving oral ORS if the person can swallow safely.

Is coconut water a good substitute for an oral rehydration solution?

Coconut water is potassium-rich and mildly hydrating; research suggests it performs comparably to sports drinks for moderate recreational exercise. However, its sodium content is very low — around 10 mmol/L — far below the 30–50 mmol/L needed for prolonged endurance work in heat or the 45–75 mmol/L in clinical ORS products. This makes coconut water inadequate as a clinical substitute for Hydralyte, Gastrolyte, or WHO ORS in acute gastroenteritis or during endurance events beyond 90 minutes in heat. It is a reasonable refreshing option for casual activity and hot-day recovery, but should not replace a clinical ORS when one is indicated.

Dehydration and electrolyte replacement

Oral rehydration therapy: when ORS helps and when water is enough

By Dr HB Lo, FACRRM Reviewed 24 October 2026 10 min read

Oral rehydration solution works by exploiting the intestinal sodium-glucose co-transporter SGLT1, which absorbs sodium and glucose together and draws water with them — making it far more effective than plain water during gastroenteritis with active diarrhoea and vomiting. Australian products Hydralyte and Gastrolyte use this mechanism.

For most healthy adults, plain water with a normal mixed diet provides all necessary electrolytes. ORS is appropriate for acute gastroenteritis, prolonged heavy sweating in heat beyond two hours, or endurance exercise beyond 90 minutes. Over-drinking plain water during endurance events risks hyponatraemia — drink to thirst rather than to a schedule.

Dehydration is the most common reason Australians reach for a sports drink, an electrolyte sachet, or an over-the-counter rehydration product. For most everyday situations — mild heat, exercise under an hour, or a hot summer afternoon — plain water combined with a normal mixed diet provides everything the body needs. However, there are genuine clinical situations where oral rehydration solution (ORS) meaningfully outperforms water alone: acute gastroenteritis, prolonged endurance exercise in heat, occupational heat exposure, and aged-care heatwave management.

The biology is straightforward. WHO reduced-osmolarity ORS works by exploiting the intestinal sodium-glucose co-transporter SGLT1, which binds one sodium ion and one glucose molecule simultaneously, transporting both into the enterocyte while water follows the osmotic gradient. This mechanism remains intact even when acute gastroenteritis disrupts other sodium-transport pathways — which is why ORS rehydrates far more efficiently than plain water during diarrhoeal illness. A 2001 systematic review in the BMJ by Hahn, Kim, and Garner — 15 randomised controlled trials and 2,397 participants — confirmed the 2002 reformulation to lower osmolarity reduced unscheduled intravenous-fluid use by 33% compared with the original 1975 formula, with less stool output and less vomiting. The reduced-osmolarity formula has been the WHO and UNICEF global standard since 2002.

A. Core clinical — the AU general-practice framework

Clinical indications for oral rehydration solution

Therapeutic Guidelines (eTG) and RACGP guidance support ORS in the following clinical contexts:

Acute gastroenteritis with any clinical dehydration — mild (increased thirst, slightly dry mouth, normal urine output) through moderate (sunken eyes, reduced skin turgor, prolonged capillary refill, oliguria) — start at symptom onset, before considering intravenous fluids.

Vomiting and diarrhoea persisting more than four hours at any age, including children and older adults.

Endurance exercise beyond 90 minutes in heat — sodium at 30–50 mmol/L in the fluid reduces the risk of dilutional hyponatraemia from over-drinking plain water.

Occupational heat exposure during prolonged shifts: per Safe Work Australia’s guide for managing heat risks, employers have a statutory duty to supply adequate cool water, shade, and structured work-rest cycles for outdoor and high-heat workers.

Multi-round sauna protocols where multiple rounds are completed with significant sweat losses between sessions.

Aged-care residents and people with cognitive impairment on hot days — impaired thirst perception means dehydration develops before the person seeks fluids.

Post-bariatric surgery dumping syndrome where fluid shifts and electrolyte losses accompany rapid nutrient transit.

When plain water is adequate

For exercise under 60–90 minutes in cool-to-temperate conditions, plain water remains the appropriate choice. The average Australian diet already provides approximately 3.2 g sodium per day — well above the NHMRC Adequate Intake of 1.6 g/day. High-sodium wellness electrolyte drinks containing 0.5–1 g sodium per serving add an unnecessary sodium load for the eutrophic adult and may destabilise blood pressure or fluid balance in people with hypertension, chronic kidney disease, or chronic heart failure.

Australian ORS product composition

Australian clinical products Hydralyte and Gastrolyte deliver sodium at approximately 45–60 mmol/L — deliberately lower than the WHO standard of 75 mmol/L — to improve palatability and paediatric oral acceptance. This modification is clinically acceptable for mild-to-moderate gastroenteritis. A DIY household ORS — one litre of clean water with six level teaspoons of sugar and half a teaspoon of table salt — approximates the WHO formula and is appropriate when commercial preparations are unavailable (for example, at a remote location or during a natural disaster).

Product	Na⁺ (mmol/L)	Osmolarity (mOsm/L)	Principal use
WHO reduced-osmolarity ORS	75	245	Severe gastroenteritis, cholera
Hydralyte (AU)	~45	~240	AU OTC gastro, paediatric
Gastrolyte (AU)	~60	~240	OTC adult/paediatric gastro
Gatorade / Powerade	~20	~330	Carbohydrate fuelling
LMNT / Liquid IV	~43–86	Variable	Wellness electrolytes (niche)
Coconut water	~10	~290	Recreational hydration

Dosing by situation

For mild-to-moderate adult gastroenteritis: small frequent sips of approximately 100 mL every 5–10 minutes, aiming for two to three litres over the first four to six hours. Per eTG for paediatric moderate gastroenteritis: 5 mL/kg every 5 minutes for one hour, then 50–100 mL/kg over four hours.

For severe dehydration at any age — altered consciousness, persistent vomiting preventing any oral intake, or profound volume depletion — intravenous normal saline (20 mL/kg bolus) is required and emergency department transfer is appropriate. Oral ORS is not suitable when the airway is not protected or the patient cannot swallow safely.

For endurance exercise beyond 90 minutes in heat: 400–800 mL per hour of fluid providing 30–50 mmol sodium per litre, taken in doses of 150–250 mL. Drink to thirst rather than to a fixed schedule.

B. Endurance hydration — sodium, hyponatraemia, and the drink-to-thirst principle

The Boston Marathon lesson

Almond and colleagues’ landmark 2005 NEJM study measured post-race sodium in 488 Boston Marathon finishers and found 13% had hyponatraemia (sodium below 135 mmol/L) and 0.6% had severe hyponatraemia (below 120 mmol/L). The primary driver was over-drinking plain water — a behaviour actively promoted by the 1990s sports-marketing doctrine of “drink before you’re thirsty.” Severe exercise-associated hyponatraemia causes cerebral oedema with presentations ranging from headache and nausea to confusion, seizure, and death.

The 2015 Third International Exercise-Associated Hyponatraemia Consensus Statement reversed this doctrine definitively: drink to thirst is now the evidence-based standard for endurance hydration. Pre-emptive over-drinking of hypotonic fluid represents a larger risk than a mild thirst-driven fluid deficit.

Sodium dose for sustained endurance

For exercise beyond 90 minutes in heat, fluid providing 30–50 mmol sodium per litre reduces the risk of dilutional hyponatraemia. Sports drinks (Gatorade, Powerade) typically provide only approximately 20 mmol sodium per litre — adequate for moderate-intensity exercise but inadequate for ultra-endurance work in heat where sweat-sodium losses are substantial. Australian ORS products (Hydralyte ~45–60 mmol/L) fall within the evidence-based range for endurance hydration.

Individual sweat-sodium variation

Baker 2017 Sports Medicine demonstrated that sweat sodium concentration varies tenfold between individuals — from 200 to 2,000 mg per litre of sweat — only modestly modified by heat acclimatisation and training. “Salty sweaters” (recognisable by white salt deposits on dark clothing, gritty skin taste, and stinging eyes) may benefit from formal sweat-sodium testing to individualise electrolyte prescription for major endurance events. Point-of-care patch tests and laboratory sweat-analysis services are available through some Australian sports-science facilities.

C. Comparing ORS, sports drinks, and wellness electrolyte products

Coconut water is potassium-rich and performs comparably to sports drinks for moderate recreational exercise, but its sodium content (~10 mmol/L) is far too low for clinical rehydration in gastroenteritis or for prolonged endurance in heat. It is a reasonable refreshing option for casual activity, not a clinical ORS substitute.

Sports drinks (Gatorade, Powerade) provide primarily carbohydrate energy with modest sodium (~20 mmol/L) — useful for fuelling exercise but insufficient as a clinical ORS substitute in gastroenteritis or for ultra-endurance sodium replacement.

High-sodium wellness electrolytes (LMNT delivers approximately 43 mmol sodium/L when made up to 500 mL; Liquid IV approximately 22 mmol/L) occupy a genuine niche in ketogenic-diet adaptation, ultra-endurance athletes, post-bariatric recovery, and post-illness fluid replacement. The marketing around them substantially exceeds the evidence for daily routine use in the general population, and their sodium content — roughly 40–100% of the daily Adequate Intake per serving — is problematic in people with blood-pressure or kidney conditions.

Sea salt and Himalayan salt are functionally identical to table salt in electrolyte terms; the trace mineral differences are clinically negligible. Iodised table salt is preferable from a population-health standpoint given the prevalence of mild iodine insufficiency in parts of Australia.

D. Australian operations

Standard GP consultations (MBS items 23, 36, 44) cover acute gastroenteritis assessment and oral rehydration counselling. Urgent urea, electrolytes, and creatinine (UEC, item 66500) is appropriate for patients with severe or prolonged vomiting and diarrhoea, significant confusion, or risk factors for electrolyte disturbance. Stool microscopy, culture, and sensitivity (MCS, item 69300) is appropriate when bacterial gastroenteritis is suspected clinically (fever, bloody stool, systemic illness, recent travel, food-poisoning cluster).

For chronic conditions where hydration planning is clinically significant — type 2 diabetes, chronic kidney disease, or chronic heart failure — the GP Chronic Condition Management Plan (items 965 and 967, replacing GPMP/TCA since 1 July 2025) enables structured hydration and dietary planning as part of multidisciplinary management.

Workplace heat obligations: Safe Work Australia places a statutory duty on employers (PCBU) to provide adequate cool water, rest breaks, shade, and Wet Bulb Globe Temperature monitoring for workers in hot environments. Sports Medicine Australia’s extreme-heat policy (v2, 2024) provides sport-specific and occupational heat thresholds for decision-making. Exertional heat stroke sustained during workplace heat exposure is compensable under state workers’ compensation schemes.

Product access: Hydralyte and Gastrolyte are generally-schedule over-the-counter products available at pharmacies and supermarkets. They are not standardly PBS-listed, though specific arrangements exist for remote Aboriginal and Torres Strait Islander health services through Section 100 community supply arrangements and for veterans through the Repatriation PBS.

Emergency presentation: ANZCOR Guideline 9.3.4 mandates cold-water immersion (neck-down, 15 minutes) before ambulance transport for exertional heat stroke — “cool first, transport second” reduces mortality from approximately 30% (when cooling is delayed beyond 30 minutes) to under 5% with rapid cooling. Intravenous normal saline and ED monitoring for rhabdomyolysis, acute kidney injury, coagulopathy, and hyperkalaemia follow.

E. Special populations

Older adults and aged care: Older people have impaired thirst perception and reduced total body water, so dehydration can develop silently before the person asks for fluids. On hot days, structured two-hourly fluid rounds, Better Health Channel heatwave guidance, and Hydralyte iceblocks for dysphagic or dementia-affected residents are appropriate proactive strategies. Routine daily ORS is not recommended — the sodium and potassium load is inappropriate for people with hypertension or chronic kidney disease.

Paediatric gastroenteritis: The evidence base for reduced-osmolarity ORS is primarily derived from paediatric trials. Small, frequent sips (5–10 mL every 2–3 minutes) using Hydralyte or Gastrolyte form the cornerstone of outpatient management per eTG. Hospitalisation thresholds include persistent vomiting preventing any oral intake for more than four hours, clinical signs of moderate-to-severe dehydration, altered level of consciousness, and poor social circumstances limiting safe home monitoring.

Chronic kidney disease and heart failure: Both conditions require careful fluid and electrolyte management. ORS for acute clinical indications (gastroenteritis, heat illness) is appropriate, but the potassium content of ORS (~20 mmol/L) requires caution in people with hyperkalaemia-prone CKD. Ongoing wellness-electrolyte supplementation should not be commenced without GP or specialist review.

Pregnancy: Hydralyte and Gastrolyte are considered safe for indicated use during pregnancy (hyperemesis gravidarum, gastroenteritis, heat exposure). Core temperature — not electrolyte levels alone — is the primary concern during heat exposure in pregnancy; a maternal core temperature above 39°C in the first trimester carries teratogenic risk and warrants urgent assessment.

People on ketogenic diets: Severe carbohydrate restriction induces urinary sodium and water loss during the first one to two weeks of adaptation, producing the “keto-flu” syndrome of fatigue, headache, and cramping. During this window, electrolyte supplementation is physiologically justified; LMNT-style products are a reasonable short-term bridge. Once dietary adaptation is complete, ongoing daily high-sodium electrolyte supplementation beyond normal dietary intake is generally unnecessary.

When to escalate

Seek emergency assessment (call 000 or attend an emergency department) for:

Confusion, collapse, or seizure associated with heat or exercise — possible exertional heat stroke; begin cold-water immersion immediately while calling 000
Inability to retain oral fluids for more than four to six hours in an infant, older adult, or person with significant comorbidity
No urine output for eight or more hours despite encouraging fluid intake
Postural dizziness or syncope on standing
Fever with bloody diarrhoea and abdominal pain — possible bacterial gastroenteritis requiring stool cultures and antibiotic assessment
Any frail older adult or infant with clinical dehydration — lower threshold for hospital assessment

For non-emergency guidance: HealthDirect 1800 022 222 is available 24 hours a day, seven days a week.

What this article is and is not

This article draws on WHO and eTG guidance, the ANZCOR and Sports Medicine Australia heat-illness frameworks, and major clinical trials in hydration physiology and endurance medicine. It is general patient information, not personalised medical advice, and does not create a doctor–patient relationship. Decisions about which fluid to use, how much, and when intravenous treatment is required are made with your treating GP or emergency team based on your individual circumstances.

For Australian consumer resources: HealthDirect — Dehydration, Better Health Channel — Heat exhaustion.

Sources cited

Frequently asked questions

When should I use Hydralyte or Gastrolyte rather than just water?

Use Hydralyte, Gastrolyte, or any oral rehydration solution when you have active gastroenteritis with diarrhoea or vomiting, when you are sweating heavily in heat for more than 90–120 minutes, or during endurance exercise beyond that threshold. For everyday drinking, mild exercise under an hour, or ordinary hot-weather exposure with a normal diet, plain water is adequate. Signs of meaningful dehydration that warrant ORS include dark urine, no urine for eight hours, dry mouth, dizziness on standing, or feeling faint — these also warrant a GP review if not improving.
What is in WHO oral rehydration solution and why does it work better than water?

WHO reduced-osmolarity ORS contains sodium 75 mmol/L, glucose 75 mmol/L, potassium 20 mmol/L, chloride 65 mmol/L, and citrate 10 mmol/L, at an osmolarity of 245 mOsm/L. It works because the intestinal sodium-glucose co-transporter SGLT1 binds one sodium and one glucose simultaneously, transporting both into the gut wall with water following the osmotic gradient. This mechanism is preserved during diarrhoeal illness when other sodium-transport pathways fail, making ORS significantly more effective than plain water. Australian Hydralyte and Gastrolyte use a slightly lower-sodium variant to improve palatability for children while retaining the same SGLT1 principle.
Can I drink too much water during exercise?

Yes — overdrinking plain water during endurance events is a documented risk. The condition is called exercise-associated hyponatraemia: when sodium falls due to excessive plain-water intake, fluid shifts into brain cells, causing headache, confusion, seizure, and in severe cases death. A 2005 NEJM study found 13% of Boston Marathon finishers had hyponatraemia after the race, primarily from drinking too much rather than too little. Current consensus is to drink to thirst. If exercising beyond 90 minutes in heat, use a fluid providing 30–50 mmol sodium per litre rather than plain water.
Should I use daily electrolyte drinks like LMNT or Liquid IV?

For most healthy Australian adults, there is no clinical need for daily high-sodium wellness electrolytes. The average Australian diet already exceeds the sodium Adequate Intake, so adding a daily serving of LMNT (approximately 1 g sodium) or Liquid IV (approximately 500 mg sodium) adds unnecessary sodium load. These products serve a genuine niche in specific situations — ketogenic-diet adaptation, ultra-endurance athletes, people with confirmed high sweat-sodium, post-bariatric surgery, post-illness recovery, or prolonged occupational heat exposure — but routine daily use in an otherwise healthy adult is not clinically justified and is contraindicated in hypertension, chronic kidney disease, and chronic heart failure.
What are the signs of heat stroke and what should I do?

Exertional heat stroke is a medical emergency requiring immediate action. Warning signs are core body temperature at or above 40°C combined with central nervous system dysfunction — confusion, slurred speech, unsteady gait, collapse, or seizure. Call 000 immediately and begin cold-water immersion (neck-down in cold or iced water) while waiting for the ambulance. Cooling before transport is the clinical priority — delay increases mortality. Less severe heat illness includes heat exhaustion (temperature 38–40°C, headache, nausea, sweating, mildly confused) and heat cramps — treated by stopping activity, moving to shade, and giving oral ORS if the person can swallow safely.
Is coconut water a good substitute for an oral rehydration solution?

Coconut water is potassium-rich and mildly hydrating; research suggests it performs comparably to sports drinks for moderate recreational exercise. However, its sodium content is very low — around 10 mmol/L — far below the 30–50 mmol/L needed for prolonged endurance work in heat or the 45–75 mmol/L in clinical ORS products. This makes coconut water inadequate as a clinical substitute for Hydralyte, Gastrolyte, or WHO ORS in acute gastroenteritis or during endurance events beyond 90 minutes in heat. It is a reasonable refreshing option for casual activity and hot-day recovery, but should not replace a clinical ORS when one is indicated.

Source quality

Sources grouped by evidence tier. AU primary tier first; international where AU is silent or lagging; named-author reconstruction where guidelines have not yet caught up. How tiers work.

T1 AU primary 8 sources
T2 International primary 1 source
- Hew-Butler et al. 2015 — 3rd International EAH Consensus
T3 Named-author reconstruction 4 sources
T4 Contrarian — examined 1 source
- WHO 2002 — Reduced-osmolarity oral rehydration salts formulation