Why do we feel thirsty?
Short answer
Thirst is the body's signal that its water balance has changed and that we may need to drink.
How it works
When we lose water, for example through sweating, there may be less water compared with salt and other substances in the blood. The amount of blood circulating may also fall. The brain senses these changes and makes us feel thirsty, encouraging us to drink.
Hormones are chemical messengers in the body. One released in response to brain signals tells the kidneys to keep more water in the body, so less water leaves in urine.
When strong thirst continues
Strong thirst that continues after drinking or comes with much more urination than usual can have causes beyond simply needing more water. Talk with a healthcare professional if this happens.