What does dehydrated mean?
Dehydrated describes something from which water has been removed, and it applies in two main ways. In reference to people and animals, it means the body has lost too much fluid — through heat, illness, exercise, or inadequate drinking — a condition that can range from mild thirst to a serious medical emergency requiring treatment. In reference to food and materials, it means moisture has been deliberately extracted, usually to preserve or lighten the product; dehydrated soups, fruits, and camping meals are familiar examples. The word derives ultimately from the Greek root hydor, meaning water, combined with the prefix de-, indicating removal. Its tone is neutral to slightly clinical when describing people — doctors say 'the patient is dehydrated' where a friend might say 'I'm parched' — and purely technical when describing goods. It contrasts with hydrated and rehydrated, which describe restoring rather than removing water.
adjectiveSuffering from or characterized by excessive loss of water from the body; also, having had moisture removed, as in food preserved by drying.
- (Of a person or living thing) having lost an excessive amount of water from the body.
- (Of food or other material) having had its natural moisture removed, typically for preservation.
"After the marathon, the exhausted runner was severely dehydrated and needed intravenous fluids."
"The hikers ran out of water and arrived at camp badly dehydrated."
"Backpackers often carry dehydrated meals because they are light and keep for years."
Your body can survive weeks without food — but just a few days without water, which is why 'dehydrated' is one of the most urgent adjectives in medicine.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dehydrated
Dehydrated comes from the verb dehydrate, formed in English from the prefix de- ('remove, reverse') plus hydrate, which itself traces back to Greek hydor, meaning water, via French and New Latin chemical usage. The verb arose in nineteenth-century scientific vocabulary as chemists needed precise terms for adding and removing water from compounds. From there it extended into physiology and food technology, with dehydrated becoming the standard participial adjective for both parched bodies and dried foods. Its cognates all descend from the same Greek root, including hydrogen ('water-former'), hydraulic, and hydration itself.
Related word forms
How dehydrated is actually used
When applied to people, 'dehydrated' is common in medical and everyday contexts alike; it is more clinical than informal words like 'parched' or 'thirsty'. Applied to food, it overlaps with 'dried' but suggests a deliberate industrial or technical process of water removal. The word carries no strong regional variation across British and American English.
Easily confused with dehydrated
Rehydrated means water has been restored to something that was dry or depleted, whereas dehydrated means water has been removed or lost.