Randomised controlled trialindependent cross-checkabstract checked I-GUT-116 in-depth review
Drinking more water reduced bladder infections
Effect of Increased Daily Water Intake in Premenopausal Women With Recurrent Urinary Tract Infections: A Randomized Clinical Trial.
Overview
Hooton TM et al.. JAMA Intern Med 2018 · PMID 30285042 · DOI 10.1001/jamainternmed.2018.4204
Women with frequent bladder infections who drank an extra 1.5 litres of water daily had about half as many infections over a year.
Does the study support the specific claim? No · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Test extra water for recurrent cystitis.
- How was the study done?
12-month RCT.
- How many people, animals or samples were studied?
140 women who drank little.
- What was actually found?
Infections fell from 3.2 to 1.7 per year.
- How large was the observed effect?
Difference 1.5 episodes (1.2-1.8).
- What do the results mean in everyday life?
For some people, drinking more than thirst suggests helps.
- What are the study's limitations?
Open label, funded by a water company.
- What does it say about Elawady's specific claim?
Contradicts 'only drink when thirsty' for everyone.
- Do the results apply to Germany and Europe?
Applicable in Europe.
- What can explicitly not be concluded from this study?
Says nothing about the liver.
Scientific in-depth review
1. Full reference
- Authors
- Hooton TM et al.
- Journal
- JAMA Intern Med
- Year
- 2018
- Identifier
- PMID 30285042 DOI 10.1001/jamainternmed.2018.4204
- Verification
- verified – PubMed efetch 2026-10-26 + Crossref 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
Funded by Danone Research (sells bottled water); four authors employed by Danone (full-text disclosure read)
2. Research question
Does drinking an extra 1.5 L of water daily reduce recurrent cystitis in premenopausal women who drink little?
3. Study design and population
- Study design
- Randomised controlled trial – Randomised, open-label controlled trial, 12 months
- Population
Healthy premenopausal women with >=3 cystitis episodes in the past year and fluid intake <1.5 L/day
- Country
Bulgaria (clinical research centre)
- Period
2013-2016
- Sample size
140 randomised
- Inclusion and exclusion criteria
Low fluid intake, recurrent cystitis
4. Methods and endpoints
- Exposure / intervention
Usual fluids plus 1.5 L water daily
- Comparator
Usual fluids only
- Endpoints
Cystitis frequency, antimicrobial courses, interval between episodes
- Statistical methods
Comparison of means with 95% CI
5. Actual results
- Results
Cystitis episodes 1.7 (1.5-1.8) vs 3.2 (3.0-3.4), difference 1.5 (1.2-1.8; P<.001); antimicrobial regimens 1.9 vs 3.6; interval 142.8 vs 84.4 days.
- Absolute risks
Total episodes 111 vs 216
- Authors' conclusion
Increased water intake is an effective antimicrobial-sparing strategy in women at high risk who drink little.
6. Strengths
- Randomised, 12 months, clear outcome
7. Weaknesses
- Open label
- Industry funded
- Selected low drinkers
8. Risk of bias
- Orienting tool
- RoB 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Open label; sponsor involvement in design.
9. Assessment of the statistical interpretation
Ratio of episodes about 0.51-0.53 (stats/C-GUT-04_07_08_misc.py).
10. Relevance to the specific claim
Shows that for some groups drinking more than habit/thirst dictates has clinical benefit; no liver harm was the topic, but the trial contradicts 'drink only when thirsty' as universal advice.
11. Independent contrary findings
Not applicable to people drinking adequately.
12. Transferability to Germany and Europe
Applicable.
13. Overall methodological judgement
Relevant counter-example to a universal thirst-only rule.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | high |
| Directness | indirect |
| Reproducibility | not replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Liver outcomes were not studied.
15. Linked fact checks
- Drinking a lot of water harms the liver; one should drink only when thirsty and not 'flood' the body with water. – Studies contradicting or limiting the claim