Water to prevent kidney stones: tap vs bottled; soft vs hard – does it matter?

Abstract

It is a question many patients ask in stone clinicdoes it matter what water I drink? Often patients cite scaling up of their water pipes or kettles as demonstrating the influence that the hardness of the water has on stone formation.Although the aetiology of urolithiasis is multifactorial, a high fluid intake is universally recommended. The recent National Institute for Health and Care Excellence (NICE) guidance on urolithiasis recommend adults drink 2.5-3 L of water per day [1]. But no guidance recommends what water is best, so does the hardness of tap water influence stone recurrence in patients with urolithiasis?What are the Differences between Hard Water and Soft Water?Tap water varies in mineral and electrolyte content dramatically between geographic areas within the same country. Water hardness is determined by the concentration of multivalent cations, predominantly calcium and magnesium. Hard water is defined as having a higher calcium carbonate (CaCO 3 ) concentration than soft water and is found in areas with chalk and limestone geology. The WHO ( https://www.who.int/water_sanitation_health/dwq/chemicals/ hardness.pdf) defines soft water as containing up to 60 mg/L CaCO 3 , whilst very hard water contains >180 mg/L CaCO 3 . CaCO 3 disassociates into Ca 2+ and CO 3 2À in the presence of dilute acid, e.g., in the digestive tract. Therefore, free Ca 2+ becomes available and contributes to daily calcium intake. How Does This Affect Urine Composition and Stone Recurrence?A double-blind, randomised crossover study of 18 calcium oxalate stone-formers (SFs) found that drinking hard mineral water (Ca 2+ 255 mg/L) was associated with a significant increase in urinary calcium concentration (although no change in oxalate excretion) compared to drinking soft mineral water (Ca 2+ 22 mg/L) or local tap water (Ca 2+ 63 AE 8 mg/L) [2]. Whether or not this in isolation influences stone recurrence is speculative. More alkaline water might be expected to increase urine citrate excretion but that did not occur in this study. Mirzazadeh et al. [3] compared 24-h urines of 15 SFs and 14non-SFs on controlled diets with soft water, moderate hardness tap water, and then mineral water. Increasing drinking water hardness increased urinary calcium levels in SFs.

Prevalence of Renal Colic in the Emergency Departments: A Multi-center Study

“…25,26 Other studies, however, consider a minimal role for the water hardness in the formation of kidney stones. 27 Although it seems irrelevant to exaggerate the role of water quality in the development of renal stones, 28 it is advisable to pay attention to water minerals in addition to their hardness. For instance, it has been noted that consuming mineral water, which is rich in minerals (especially bicarbonate), can influence the formation of kidney stones.…”

An investigation into the potential anticaries benefits and contributions to mineral intake of bottled water

“…Water hardness has been negatively related to risk of cardiovascular disease, although the evidence is controversial. 33 The consumption of hard water also has the potential to provide essential minerals, such as calcium and magnesium, which support critical metabolic functions and bone health. 14 With our study we also wanted to investigate whether bottled water can provide meaningful contributions to intakes of fluoride, calcium, magnesium, potassium and sodium (table 3).…”

Nutrition and Kidney Stone Disease

“…The impact of the composition of tap water and mineral water on kidney stone formation is still a matter of debate. The composition of drinking water, predominantly the content of the divalent cations calcium and magnesium, varies widely between geographic regions within the same country [35]. Hard tap water, defined as a calcium carbonate concentration above 120 mg/L [36], can contribute to the daily dietary calcium intake.…”