Do you need to drink 8 glasses of water a day?

MIXED EVIDENCE
18 relevant RCTs from 183+ studies PubMed results Last checked May 2026
While increased water intake shows some health benefits, the '8 glasses a day' rule lacks strong scientific backing for the general population.
Clinical trials show that increased water intake can provide specific health benefits like weight loss, kidney stone prevention, and reduced urinary tract infections. However, there's limited high-quality evidence supporting the universal '8 glasses daily' recommendation for healthy adults. The optimal amount varies based on individual needs, health conditions, and activity levels.
Overall confidence
70%
RCT quality
65%
Expert consensus
60%
RCTs found
18 relevant RCTs from 183+ studies
Largest trial
140 participants
Date range
2007–2024
Effect size
small to moderate
Key studies
JAMA Network Open systematic review · 2024
Limited RCTs show benefits for weight loss and kidney stones, but evidence quality is limited
PubMed 39585691 ↗
JAMA Internal Medicine UTI trial · 2018
1.5L additional water daily reduced recurrent UTIs by 50% in at-risk women
PubMed 30285042 ↗
Nutrients Japanese cohort · 2020
Extra 1.1L daily lowered blood pressure and improved kidney markers in healthy adults
PubMed 32340375 ↗
Caveats
Most studies tested specific additional water amounts rather than the '8 glasses' rule, and benefits were often seen in people with specific conditions or low baseline intake

People also ask

Is 8 glasses of water daily necessary for everyone?
No universal evidence supports this; individual needs vary based on activity, climate, and health status
What health benefits does increased water intake provide?
Studies show benefits for weight management, kidney stone prevention, and UTI reduction in specific populations
How much water should I actually drink?
Listen to thirst, ensure adequate hydration, and consider increasing intake if you have specific health conditions
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Bust your myth →
BustMyMyth synthesizes published RCT evidence. It is not medical advice. Always consult a qualified healthcare professional. Sources: PubMed/MEDLINE, Cochrane Library, ClinicalTrials.gov.