Survival times without water & food
Last reviewed on 30.06.2026
As a rule of thumb, a person survives without water about 3 days, without food about 3 weeks – the «Rule of Threes». In reality it varies widely: without water depending on heat and exertion about 2 to 7 days, without food with sufficient water up to about 70 days. Water therefore always takes priority. In acute emergency: call 144.
How long can a person survive without water and without food? The well-known rules of thumb – about 3 days without water, about 3 weeks without food – are rough guides, not guaranteed figures. Above all, they show why water always takes priority over food in an emergency.
Important note
This article is for general information only and does not replace medical advice. The times mentioned are rules of thumb and vary greatly from individual to individual. If signs of severe dehydration or malnutrition appear – confusion, impaired consciousness, circulatory weakness – call the emergency medical number 144 immediately. In case of suspected poisoning, Tox Info Suisse helps around the clock on 145.
How long can humans survive without water and food?
Without water: The rule of thumb states about 3 days. In reality it depends heavily on temperature and exertion – in heat and under physical strain only hours to about a day, in a cool environment and at rest over a week. A range of about 2 to 7 days is typical. Children, the elderly and sick people, and those with vomiting or diarrhoea are particularly at risk.
Without food: With sufficient water, the body lasts much longer. The rule of thumb states about 3 weeks; extreme cases of over 70 days are documented under medical supervision (in one individual case up to 382 days with vitamins – not a benchmark). Without water this time drops dramatically.
Water requirement: For drinking alone a person needs about 2.5 to 3 litres per day. The WHO emergency standard assumes at least 15 litres per person per day (incl. hygiene and cooking); an absolute survival minimum is about 7.5 litres. The federal government recommends 9 litres of drinking water per person as supplies for about three days.
What is the Rule of Threes?
The «Rule of Threes» is a memory aid for the priority order in an emergency: about 3 minutes without air, about 3 hours without protection from extreme weather, about 3 days without water and about 3 weeks without food. The figures are rough estimates, not exact limits – they mainly show: breathing and warmth come before water, water comes before food.
The reason for the first step: without oxygen a person loses consciousness after about 10 to 15 seconds, and from around 4 to 5 minutes there is a risk of irreversible brain damage. The «3 minutes» are therefore not a buffer but a call to action – in the event of respiratory arrest, start chest compressions immediately and alert the emergency medical number 144.
How do I recognise dehydration?
Water loss makes itself felt early. A simple early indicator is urine colour: the aim is a pale yellow. The stages below are guide values – if in doubt and with severe signs: call 144.
| Severity | Water loss (% body weight) | Possible signs |
|---|---|---|
| Mild | approx. 3–5% | thirst, dark urine, reduced performance (often from 1–2%) |
| Moderate | approx. 6–10% | reduced skin turgor, rapid pulse, headache, much less urine |
| Severe | over 10% | confusion, shock, unconsciousness – life-threatening, call 144 immediately |
The percentage values primarily come from paediatrics; in adults the thresholds may be lower. Infants, children and the elderly are particularly at risk. Electrolytes/ORS should be part of your supplies.
What happens in the body during starvation
Without food, the metabolism switches in stages: first sugar reserves (glycogen) are used (~0–24 hours), then the body forms new glucose (24–48 hours), from about 48 hours it increasingly meets needs through fat (ketosis, protein-sparing). In the most dangerous late stage the body breaks down muscle protein. Signs include weight and muscle loss, feeling cold, susceptibility to infection, oedema and apathy.
Warning refeeding syndrome: after prolonged starvation you must not eat too quickly again. The sudden nutrient boost can upset the mineral balance (hypophosphataemia) and lead to life-threatening heart rhythm disorders. Refeeding after prolonged starvation must be medically supervised.
Frequently asked questions
How long can you survive without water?
As a rule of thumb about 3 days. In reality it depends heavily on temperature and exertion: in heat and under physical strain only hours to about a day, in a cool environment and at rest over a week. Typically about 2 to 7 days. Children, the elderly and sick people are particularly at risk.
How long can you survive without food?
With sufficient water much longer than without: the rule of thumb says about 3 weeks; extreme cases of over two months are documented under medical supervision. Without water this time drops dramatically. After prolonged starvation, because of refeeding syndrome, you must not eat too quickly.
What does the Rule of Threes mean?
A memory aid for priorities in an emergency: about 3 minutes without air, about 3 hours without protection from extreme weather, about 3 days without water and about 3 weeks without food. The figures are rough values and mainly show the order.
How much water does one need per day in an emergency?
For drinking alone about 2.5 to 3 litres per day. The WHO emergency standard assumes at least 15 litres per person per day including hygiene and cooking; an absolute survival minimum is about 7.5 litres. The federal government recommends 9 litres of drinking water per person for about three days.
Why must you start resuscitation immediately in the event of respiratory arrest?
Because the brain stays conscious for only seconds without oxygen: loss of consciousness occurs after about 10 to 15 seconds, and irreversible brain damage begins from around 4 to 5 minutes. That is why air comes first in the «Rule of Threes» – with chest compressions and the emergency call 144, every second counts.
Official sources
- FOPH Federal Office of Public Health
- Tox Info Suisse Emergency number 145 if poisoning suspected
- Guide: Build an emergency supply Store water and food
- Guide: Make drinking water safe Drinking water safely in an emergency
- Emergency supply calculator Calculate water and food requirements for your household