After a kidney stone, drink 2.5–3 liters of water a day and cut salt to within 6 grams

Among people who grew a first calcium stone and no cause was found, about a quarter grow another within 5 years if they do nothing. Among people who drink enough water every day, a bit over a tenth have a recurrence within 5 years, fewer by more than half. The British guideline gives 2.5 to 3 liters of water a day, and salt no more than 6 grams.

Cost

No cost. Make drinking whenever you can into a habit. On days you sweat a lot, drink still more. The hard part is remembering every day.

Benefit

A 5-year randomized controlled trial in 199 patients with a first calcium stone and no cause found (also called idiopathic calcium stones). The water group drank at least 2 liters of water a day; the other group had no intervention. Recurrence over 5 years: 12/99 (12.1%) in the group that drank more water, 27/100 (27.0%) in the group with no intervention, P=0.008. A smaller P value means the difference between the groups is less likely to be chance. Mean time until recurrence: 38.7±13.2 months versus 25.1±16.4 months, P=0.016. The 24-hour urine volume measured at the start was clearly lower in stone patients than in people without stones: men 1057±238 mL versus 1401±562 mL (P<0.0001), women 990±230 mL versus 1239±440 mL (P<0.001). Clause 1.8.1 of NICE guideline NG118 recommends that adults drink 2.5 to 3 liters of water a day, and that children and adolescents drink 1 to 2 liters by age. Add a little fresh lemon juice to the water, do not drink carbonated drinks, and keep salt for adults to no more than 6 grams a day. Clause 1.7.1 of the same NICE guideline recommends considering a stone composition analysis for adults who have had a kidney stone or a ureteral stone. For people with recurrence whose stone is more than half calcium oxalate, clause 1.8.3 recommends considering potassium citrate. NICE found no evidence on 24-hour urine testing and gives no recommendation. The stone guideline of the European Association of Urology (EAU) is written differently: every patient with a stone should have a reliable stone composition analysis. People with recurrence count as high risk and should give 24-hour urine twice in a row for a dedicated metabolic workup. Its general prevention target is 2.5 to 3 liters of water a day, and a daily urine volume of 2 to 2.5 liters

Notes

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

Sources · 3

1. 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. doi.org/10.1016/s0022-5347(01)66321-3
2. 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. nice.org.uk/guidance/ng118/chapter/Recommenda…
3. 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）. uroweb.org/guidelines/urolithiasis/chapter/me…（高危结石患者名单见同一指南 Table 3.3：uroweb.org/guidelines/urolithiasis/chapter/gu…）