People who have had kidney stones should drink 2.5–3 liters of water daily and keep salt intake under 6 grams

There is no cost at all. Simply make drinking water a daily habit. On days when you sweat a lot, you’ll need even more water — the hard part is remembering to do this every day.

In a 5-year randomized controlled trial of 199 patients with a first episode of unexplained calcium kidney stones (idiopathic calcium stone disease), one group increased water intake to achieve a daily urine volume of at least 2 liters, while the other received no intervention. Over 5 years, recurrence occurred in 12/99 (12.1%) in the increased water group versus 27/100 (27.0%) in the no-intervention group (P = 0.008; a smaller P value indicates the difference between groups is less likely due to chance). The average time to recurrence was 38.7 ± 13.2 months versus 25.1 ± 16.4 months (P = 0.016). Baseline 24-hour urine volume was significantly lower in stone formers than in healthy controls: 1,057 ± 238 mL versus 1,401 ± 562 mL in men (P < 0.0001), and 990 ± 230 mL versus 1,239 ± 440 mL in women (P < 0.001). NICE guideline NG118 (recommendation 1.8.1) advises adults to drink 2.5 to 3 liters of water daily, and children and adolescents 1 to 2 liters depending on age, with added fresh lemon juice, avoiding carbonated drinks, and restricting adult salt intake to no more than 6 grams per day. Recommendation 1.7.1 in the same guideline advises considering stone composition analysis for adults with a history of renal or ureteric stones. For recurrent stone formers whose stones contain more than 50% calcium oxalate, recommendation 1.8.3 advises considering potassium citrate. NICE found insufficient evidence to recommend routine 24-hour urine testing. The European Association of Urology (EAU) guideline takes a different approach: every stone patient should undergo reliable stone analysis. Recurrent stone formers are classified as high risk and should collect two consecutive 24-hour urine samples for specialized metabolic evaluation. The EAU general prevention target is drinking 2.5 to 3 liters of fluids daily with a daily urine output of 2 to 2.5 liters.

Bao Y, Tu X, Wei Q (2020). Water for preventing urinary stones（纳入研究 Borghi 1996 的干预目标为尿量至少 2 L/日）. Cochrane Database of Systematic Reviews, 2, CD004292. https://pmc.ncbi.nlm.nih.gov/articles/PMC7012319/；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，第 1.7.1、1.8.1、1.8.3 条. https://www.nice.org.uk/guidance/ng118/chapter/Recommendations；European Association of Urology (2026). EAU Guidelines on Urolithiasis, Chapter 4 Metabolic Evaluation and Recurrence Prevention（第 4.1、4.1.2 节，Table 4.5）. https://uroweb.org/guidelines/urolithiasis/chapter/metabolic-evaluation-and-recurrence-prevention（高危结石患者名单见同一指南 Table 3.3：https://uroweb.org/guidelines/urolithiasis/chapter/guidelines）

Recurrence was about 55% lower, and it costs nothing, so by this book's way of scoring value for money this is the highest-value item in the section. What to watch is 24-hour urine volume. The European guideline's target is 2 to 2.5 liters a day, not how much you drink. People who sweat a lot, and people who work in high heat, have to drink more. That trial enrolled patients with a first episode of idiopathic calcium stones. There is more than a single stone type: uric acid stones, infection stones, and cystine stones each have their own approach. Both the British and the European guidelines recommend a stone composition analysis. For people who have recurred, the European guideline also requires a 24-hour urine test before deciding whether to add a drug; the British guideline finds the evidence for that test insufficient. Do not cut out calcium to prevent stones; see section 6, item 21. Severe colic in the flank or abdomen during an attack means go to a hospital, not try to flush the stone out by drinking more. Painless blood in the urine has other things that need checking; see section 1, item 27