On this page
Dr. Chrysoula I. Liakou MD, PhD
- Treated online: Yes, for mild to moderate cases; emergency signs need in-person fluids.
- Mild to moderate dehydration is treated with oral rehydration solution taken in small, frequent sips; confusion, drowsiness or passing no urine are emergency signs.
- Urine colour is the everyday gauge of hydration: pale straw means well hydrated, amber to brown means drink more.
- Diuretics, some diabetes and blood pressure medicines and lithium raise dehydration risk, but never stop prescribed medicines without advice.
- Babies dehydrate much faster than adults, so more than the mildest signs mean in-person medical care the same day, not watchful waiting.
Get emergency in-person care now, or call 112, for confusion or unusual drowsiness, no urine for 8 hours or more, fits, or cold, mottled hands and feet. Babies with a sunken soft spot on the head, no wet nappy for many hours, or listlessness, and elderly people who become confused or stop drinking, need urgent in-person care today, not a video call.
Can an online doctor treat dehydration?
Yes, for mild to moderate cases. The doctor builds an oral rehydration plan, treats the cause where one is found, such as vomiting or diarrhoea, and tells you plainly when the signs point to in-person care and intravenous fluids instead.
How do I know if I am dehydrated?
The reliable signs are thirst, dark yellow urine passed less often than usual, a dry mouth and lips, headache, tiredness and feeling lightheaded when standing up.[5] Urine colour is the everyday gauge: pale straw means hydrated, amber to brown means drink more. In babies, fewer wet nappies and a sunken soft spot matter most; in older adults, new confusion may be the first sign.[2] Severity ranges widely, and the treatment depends on it.
How an online consultation helps with dehydration
- Severity triage you cannot easily do yourself: the doctor tallies fluid in versus fluid out, checks urine colour and frequency, watches for dizziness on standing, and places you honestly on the home-versus-hospital line.
- Treating the cause, not just the dryness: most dehydration follows vomiting and diarrhoea; the doctor treats the gut illness where appropriate, including anti-sickness medication that can keep oral rehydration possible.
- A medication safety review: water tablets, some diabetes and blood pressure medicines and lithium can turn a routine stomach bug into a dangerous one; the doctor tells you what to pause and what never to pause on sick days.
- Rehydration technique that actually works: what to drink, how much, how fast, and the small-sips method that keeps fluid down even in someone who is vomiting.
What causes dehydration?
Illness: the biggest cause
Vomiting and diarrhoea drain both water and salts faster than casual drinking replaces them, which is why gastroenteritis is the leading cause of significant dehydration at every age.[1] Fever compounds it: every degree of temperature increases fluid loss through skin and breath. Most gut infections are viral, so antibiotics are only prescribed when there are genuine signs of bacterial infection; what changes the outcome is rehydration, started early and done properly.[1] Persistent diarrhoea that outlasts the usual few days deserves its own assessment rather than ever-larger drinks.
Heat, exercise and travel
Heatwaves, unaccustomed southern European summers, long hikes and flights all raise losses, and heat kills mainly through dehydration and heat exhaustion in people who did not notice it happening, particularly older adults whose thirst signal weakens with age.[3] In hot weather, drink before thirst arrives, salt your food normally, and treat headache with dizziness after heat exposure as a warning to cool down and rehydrate now. Alcohol in the sun is a double loss: it increases urine output while you sweat.
Medicines that dry you out
Diuretics (water tablets) do their job regardless of whether you are losing fluid elsewhere; laxatives, SGLT2 diabetes tablets (the gliflozins) and excess caffeine add to losses; and lithium becomes more concentrated and more toxic as you dry out. During any vomiting-and-diarrhoea illness, some medicines usually need a temporary pause (commonly diuretics, ACE inhibitor blood pressure tablets, anti-inflammatory painkillers and metformin) precisely because they become harmful in a dry body, but that decision belongs in a consultation, not a guess: never stop prescribed medicines without medical advice.[2]
How do you rehydrate properly?
Plain water is enough for mild thirst after a warm day. Once losses are real (repeated diarrhoea, vomiting, heavy sweating), water alone replaces the volume but not the salts, so the standard treatment is oral rehydration solution (ORS): pharmacy sachets containing a precise ratio of glucose and salts that the gut absorbs faster than either alone, the same principle WHO credits with saving millions of lives in diarrhoeal illness.[1] Practical technique matters as much as the sachet:
- Small and frequent beats large and rare: a few sips every five minutes stays down even in someone who is vomiting; a full glass often comes straight back. For children, a teaspoon or syringe every couple of minutes works.
- Dose by losses: as a rule of thumb, roughly a cup (200 ml) of ORS after each loose stool for an adult, on top of normal drinking; children need proportionally less, per the sachet instructions.[1]
- Keep eating as tolerated: starving yourself does not rest the gut; light food as appetite returns speeds recovery. Breastfed babies should continue feeding throughout, with ORS between feeds.
- Choose fluids wisely: avoid undiluted fruit juice, sugary soft drinks and alcohol, which can worsen diarrhoea; strong caffeine adds to urine losses. Flat soft drinks are not a substitute for ORS, whatever tradition says.
- Mix sachets exactly: with the stated volume of drinking water, never stronger, and use boiled or bottled water where tap water is unsafe.
Preventing it in the first place
Prevention is mostly anticipation. Pre-hydrate before long flights, hikes and hot days rather than chasing thirst afterwards; pack ORS sachets when travelling somewhere hot or somewhere stomach bugs are likely, because buying them mid-illness in an unfamiliar pharmacy is nobody's best moment; and during religious or intermittent fasting, front-load fluids in the permitted window. Moderate caffeine, for regular drinkers, is not meaningfully dehydrating despite its reputation; alcohol genuinely is. For anyone caring for a frail relative through summer, a filled glass within reach beats any amount of reminding.
When can dehydration be managed at home?
Swipe sideways to compare →
| Presentation | Likely first step | Suitable for online care? | When referral or in-person care is needed |
|---|---|---|---|
| Thirsty, dark urine, otherwise well (mild) | Fluids and ORS at home, cause addressed | Yes | If not clearly improving within a day, or losses continue |
| Gastroenteritis with repeated vomiting, struggling to keep fluids down | Assessment, small-sips ORS technique, anti-sickness medication where appropriate | Often yes | Nothing kept down for 24 hours, or signs of worsening dryness |
| Frail, elderly, or on diuretics or diabetes medicines, with a fluid-losing illness | Early review, sick-day medication adjustments, close safety-netting | Yes, early and deliberately | Deterioration, new confusion, or reduced urine despite fluids: same-day in-person care |
| Baby or young child with fewer wet nappies, dry mouth, unusual sleepiness | In-person assessment today | No, beyond initial advice | Immediately; children dehydrate faster than adults[4] |
| Confusion, drowsiness, no urine for 8+ hours, cold mottled skin, fits | Emergency care; intravenous fluids are likely | No | Call 112 now |
Availability of individual medicines and who may prescribe them vary by country; your doctor confirms what applies where you are.
Not sure which row is you? A doctor can tell you in one consultation.
See available times →What the doctor checks in an online dehydration consultation
Dehydration assessment is mostly structured history, which video handles well. The doctor will typically check:
- The fluid balance sheet: what has gone in and what has come out over the last 24 hours, counted honestly: episodes of vomiting and diarrhoea, sweating, and every drink.
- Urine as the gauge: colour, how often, and when you last passed a good volume; a long dry gap is a hard warning sign.
- How you behave on camera: alertness, speech, and dizziness on standing (the doctor may ask you to stand during the call, which is a crude but useful orthostatic test).
- The cause: gut infection, heat exposure, poorly controlled diabetes (thirst plus large urine volumes is the opposite pattern and needs testing), or a medicine doing its job too well.
- Your risk multipliers: age at both extremes, frailty, pregnancy, kidney disease, diabetes and the medication list, which decide how early to escalate.
- Red flags in the room: for a child or elderly relative, the doctor coaches you through checks on camera: skin pinch, dry tongue, sunken eyes, wet-nappy count.
When we treat dehydration online, and when we refer you
We treat online: mild to moderate dehydration in otherwise healthy people, with an ORS plan and a review point; the underlying gastroenteritis, including anti-sickness medication where clinically appropriate; sick-day medication adjustments for people on diuretics, blood pressure or diabetes tablets; heat-related fluid loss with a cooling and rehydration plan; and prevention planning for people who dehydrate repeatedly, from athletes to carers managing a frail relative at home.
We refer or redirect you: anyone with emergency signs (confusion, drowsiness, no urine for 8+ hours, fits, cold mottled skin) straight to emergency care, because that person needs intravenous fluids, not advice; babies and young children with more than the mildest signs, same day and in person; suspected new diabetes, kidney problems or bowel disease behind the fluid loss, with tests arranged and a clear handover; and vomiting that keeps everything down for a day or more despite correct technique. If we send you onward, you are told exactly why and with what urgency.
When to get in-person care
Call 112 or go to emergency care immediately for confusion or unusual drowsiness, fits, no urine for 8 hours or more, a weak rapid pulse, or cold, mottled hands and feet.[5] For babies: a sunken soft spot, no wet nappies for several hours, listlessness or a weak cry mean urgent in-person care now. For elderly people: new confusion or refusing fluids during illness or a heatwave is an emergency of quiet onset; act the same day.
How Mobi Doctor works
- Book a time that suits you: open daily 7am–11pm. Most patients speak to a doctor within about 15 minutes of their booked time. no subscription, exact price up front.
- Speak to a licensed doctor about dehydration: a private video call: you describe what you feel, the doctor asks what matters, and you agree the right plan together.
- Get your rehydration plan and treatment for the cause: a prescription follows the consultation when it is right for you. If we can’t help you online, you get a full refund.
No sign-up needed
Dehydration care across the EU
Oral rehydration salts are sold in every EU pharmacy without a prescription, under a different name in nearly every country, so ask the pharmacist for rehydration sachets rather than a brand. Southern Europe's summer heat waves make dehydration one of the most common holiday illnesses, especially in children and older adults.
If drinking is not staying down, or someone is drowsy, confused or passing very little urine, that is beyond home care. A doctor on video can help you judge how serious it is and where to go if it needs more than fluids.
Tick what you feel to see every condition page that mentions it. It finds the right page, not a diagnosis: a doctor gives you that on a video call.
Not sure this is the right page? Find your symptom in the symptom navigator, or book and describe it to a doctor.
Frequently asked questions about dehydration
Can an online doctor treat dehydration?
Yes, when it is mild to moderate: the doctor assesses severity by structured questions and video, treats the cause such as gastroenteritis, adjusts medicines that worsen fluid loss, and gives you an exact rehydration plan. Severe dehydration needs intravenous fluids in hospital, and the assessment is honest about which side of the line you are on.
How much does a consultation cost, and how fast can I be seen?
The exact price of a video consultation is shown before payment, and there is no subscription. Appointments are available daily from 7am to 11pm, often within about 15 minutes, which matters with dehydration because early advice usually keeps it manageable at home.
What is the best drink for dehydration?
For real losses from diarrhoea, vomiting or heavy sweating, oral rehydration solution from a pharmacy is the evidence-based choice: its glucose-and-salt mix is absorbed faster than water alone. Plain water is fine for mild thirst. Avoid undiluted juice, sugary soft drinks and alcohol, which can make diarrhoea and fluid loss worse.
How much water should I drink a day?
There is no magic universal number: needs vary with body size, climate, activity and illness. A practical target is drinking enough that your urine stays pale straw coloured through the day. Needs rise sharply in heat, fever and gut illness, which is when deliberate rehydration replaces casual sipping.
What are the signs of dehydration in a baby?
Fewer wet nappies than usual, a dry mouth, a sunken soft spot on the head, sunken eyes, unusual sleepiness or irritability, and crying with few tears. Babies dehydrate much faster than adults, so more than the mildest signs mean in-person medical care the same day, not watchful waiting.
My elderly parent will not drink during a heatwave. What should I do?
Take it seriously: thirst weakens with age, and confusion can be the first sign of trouble. Offer small drinks constantly rather than big glasses, include soups, yoghurt and fruit, keep rooms cool, and get medical advice early, especially if they take water tablets or blood pressure medicines. New confusion or refusal to drink is a same-day emergency.
When does dehydration need a drip?
When fluids cannot go in by mouth as fast as they are being lost, or the body is visibly failing: confusion, drowsiness, no urine for 8 hours or more, a weak rapid pulse, or vomiting that rejects even small sips for a day. Those situations need hospital assessment and intravenous fluids, and no online service should suggest otherwise.
- Diarrhoeal disease: fact sheet, WHO, World Health Organization, 2024.
- Gastroenteritis: Clinical Knowledge Summary, NICE Clinical Knowledge Summaries, revised 2024.
- Heat and health: fact sheet, WHO, World Health Organization, 2024.
- Diarrhoea - adult's assessment: Clinical Knowledge Summary, NICE Clinical Knowledge Summaries, revised 2023.
- Dehydration in adults, HSE, Health Service Executive Ireland, 2025.
This page is for information only and is not a substitute for a medical consultation. Guideline links are provided for transparency; treatment decisions are made with your doctor.
Related conditions
From the Mobi Doctor blog
Dehydration Headaches: Symptoms, Treatment, And Prevention
A dehydration headache develops when your body loses more fluid than it takes in, reducing normal hydration and triggeri...
Read article → Health and WellbeingWhat Is the Best Travel Insurance for Europe?
There is no single best travel insurance policy for Europe. The right policy depends on your destination, trip length, m...
Read article → Health and WellbeingHow to See a Doctor While Travelling in Europe
If you become ill while travelling in Europe, the best option depends on your symptoms and how urgently you need ur...
Read article →From the Mobi Doctor podcast
The 10 Most Common Travel Illnesses
The travel illnesses doctors see most often in Europe, and how to handle each one away from home.
Listen · 23 Feb 2026 → Podcast · 13:26How to Stay Healthy on a Long Flight
Practical steps for circulation, hydration and infection risk before, during and after a long flight.
Listen · 23 Feb 2026 → Podcast · 15:41Debunking Gut Health Myths
What the evidence really says about gut health, and the popular claims that do not hold up.
Listen · 23 Feb 2026 →Speak to a doctor about dehydration today
Licensed doctors · open daily 7am–11pm · exact price before payment
See available times →