Does everyone need exactly eight glasses of water a day?
Eight glasses is not a compulsory amount for everyone. Needs vary with body size, activity, heat, pregnancy and illness, and food and drinks contribute to hydration. Some heart or kidney conditions require individualized fluid plans rather than automatic increases.
Details
Use practical clues
Drink regularly and notice thirst, urine colour and amount. Pale-yellow urine is a rough guide, not an independent test. Medicines and vitamins can change colour, and some older adults have reduced thirst.
Adjust to circumstances
Sweating, heat or illness may increase needs. Vomiting and diarrhoea may require appropriate oral rehydration rather than water alone. Do not force large volumes rapidly, and follow any prescribed fluid limit.
When to seek help
Markedly reduced urine, persistent dizziness or inability to retain fluids needs assessment. Confusion, severe drowsiness or rapid deterioration requires urgent care, particularly in children and older adults.
Related reading: Why do I feel dizzy when standing up, and when should it be checked?.