If you have had a kidney stone, drink 2.5–3 liters of water a day and keep salt to no more than 6 grams

Cost

Free. Make drinking water through the day a habit. On days you sweat a lot, drink more. The hard part is remembering every day.

What you get

A 5-year controlled trial with random assignment to two groups, in 199 patients with a first calcium stone and no identifiable cause (also called idiopathic calcium stones). One group drank at least 2 liters of water a day, and the other did nothing. Recurrence within 5 years was 12/99 (12.1%) in the extra-water group and 27/100 (27.0%) in the no-intervention group, P=0.008. The smaller the P value, the less likely the difference between the two groups is chance. Average time to recurrence: 38.7±13.2 months versus 25.1±16.4 months, P=0.016. In the 24-hour urine volume measured at the start, stone patients were clearly lower than people without stones: for men 1,057±238 mL versus 1,401±562 mL (P<0.0001), and for women 990±230 mL versus 1,239±440 mL (P<0.001). Clause 1.8.1 of the NICE guideline NG118 recommends that adults drink 2.5 to 3 liters of water a day and that children and teenagers drink 1 to 2 liters depending on age. Add a little fresh lemon juice to the water, avoid fizzy drinks, and keep adults' salt to no more than 6 grams a day. Clause 1.7.1 of the same NICE guideline recommends that adults who have had a kidney or ureteral stone consider having the stone's composition analyzed once. For recurrent stones that are more than half calcium oxalate, clause 1.8.3 recommends considering adding potassium citrate. NICE found no evidence for the 24-hour urine test and made no recommendation. The stone guideline of the European Association of Urology (EAU) is written differently: every stone patient should have a reliable stone composition analysis. People with recurrences are high risk and should collect two consecutive 24-hour urine samples for a specialized metabolic work-up. Its general prevention target is 2.5 to 3 liters of water a day, with a urine volume of 2 to 2.5 liters a day

Notes

Recurrence fell by about 55%, and it costs nothing, so under this book's ranking rule this is the best value in the section. What to watch is the 24-hour urine volume, with the European guideline's target being 2 to 2.5 liters a day, not how much you drink. People who sweat a lot or work in high heat need to drink even more. That trial was in patients with a first idiopathic calcium stone. Stones are not all of one kind, and uric-acid stones, infection stones and cystine stones each have their own measures. Both the British and European guidelines recommend a stone composition analysis. For people who have had a recurrence, the European guideline also requires a 24-hour urine test before deciding whether to add medicine, while the British guideline considers the evidence for this test insufficient. Don't give up calcium to prevent stones; see §6.21. If you get severe cramping pain in your side or abdomen during an attack, go to the hospital; drinking more water will not wash the stone out. Painless blood in the urine has other causes that need checking; see §1.27

Evidence grade

A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.

Sources

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. https://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, items 1.7.1, 1.8.1, 1.8.3. https://www.nice.org.uk/guidance/ng118/chapter/Recommendations
3. European Association of Urology (2026). EAU Guidelines on Urolithiasis, Chapter 4 Metabolic Evaluation and Recurrence Prevention (Sections 4.1 and 4.1.2, Table 4.5). https://uroweb.org/guidelines/urolithiasis/chapter/metabolic-evaluation-and-recurrence-prevention (the list of high-risk stone patients is in Table 3.3 of the same guideline: https://uroweb.org/guidelines/urolithiasis/chapter/guidelines)

Translated from the Chinese original. Original book, section 16, tip 8. This section is about health and medicines. It is general information, not a substitute for a doctor’s diagnosis or prescription. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer