After kidney stones, discuss sufficient fluid to produce ample urine and keep salt below 6 grams daily
Among first-time calcium-stone patients in one trial, recurrence over 5 years was about one-quarter without intervention and just over one-tenth with increased water—more than halved. UK NICE guidance recommends 2.5–3 liters of water a day for adults and no more than 6 grams of salt.
What it takes
No significant extra cost. Make drinking regularly a habit and increase intake with heavy sweating.
What you may gain
A five-year randomized trial included 199 first-time idiopathic calcium-stone patients, meaning no specific cause was identified. One group drank at least 2 liters daily and the other received no intervention. Recurrences were 12/99 (12.1%) versus 27/100 (27.0%), P=0.008. A smaller P value indicates less compatibility with chance alone under the tested null hypothesis. Mean recurrence intervals were 38.7±13.2 versus 25.1±16.4 months, P=0.016. Baseline 24-hour urine volume was lower in stone patients than controls: men 1,057±238 versus 1,401±562 mL (P<0.0001), women 990±230 versus 1,239±440 mL (P<0.001). NICE NG118 recommendation 1.8.1 advises adults to drink 2.5–3 liters of water daily, children/adolescents 1–2 liters depending on age, add fresh lemon juice, avoid carbonated drinks and limit adult salt to 6 grams daily.
Context & considerations
About 55% fewer recurrences at little cost makes this highly ranked by the book's method. The practical target is 24-hour urine output of at least about 2–2.5 liters, not just fluid swallowed; heavy sweating and hot work require more intake. The trial concerned first-episode idiopathic calcium stones. Uric-acid, infection and cystine stones have different management. Recurrent stones merit composition analysis and a 24-hour urine test to guide medication. Do not eliminate dietary calcium to prevent stones; see Chapter 6, entry 21. Severe renal colic needs medical care rather than trying to flush a stone with water. Painless blood in urine needs separate evaluation; see Chapter 1, entry 27.
Research & references
Borghi L, Meschi T, Amato F, Briganti A, Novarini A, Giannini A (1996). Urinary volume, water and recurrences in idiopathic calcium nephrolithiasis: a 5-year randomized prospective study. The Journal of Urology, 155(3), 839-843. https://doi.org/10.1016/s0022-5347(01)66321-3; National Institute for Health and Care Excellence (2019). Renal and ureteric stones: assessment and management. NICE guideline NG118, recommendation 1.8.1. https://www.nice.org.uk/guidance/ng118/chapter/Recommendations