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What is the position on kidney stones and hard or softened water?

Several studies have been conducted around the above question, but these appear contradictory. The NHS website certainly makes no link between hard water and kidney stones.

We will update this page as more information on this subject is released. However, here follows other sites that may be of interest in your search for the facts.

Over the years, the industry has referred to various studies with one such non-specific reference: What Does Water Treatment and Kidney Stones Have in Common?

The US National Library of Medicine states "As compared with both tap and soft water, hard water was associated with a significant 50% increase of the urinary calcium concentration in the absence of changes of oxalate excretion; the calcium-citrate index revealed a significant threefold increase during ingestion of hard water as compared with respect to soft water (Fiuggi water), making the latter preferable even when compared with tap water. This study suggests that, in the preventive approach to calcium nephrolithiasis, the extra meal intake of soft water is preferable to hard water, since it is associated with a lower risk for recurrence of calcium stones."

There are several websites that discuss the question of hard water and kidney stones, and several state that there is no link, including Does Hard Water Cause Kidney Stones?

Myth or Reality – Are Kidney Stones Caused by Hard Water? states "Very high hardness (above 300 PPM) which is not typical of drinking water originating from surface water and may be associated with a higher risk of kidney stones. In most cases of kidney stones, the blood in a human body, due to certain inherent problems, starts absorbing more calcium from water and food than actually needed. As a result, excess calcium is deposited on the walls of the kidney in the excretion process." Water hardness in Kent, Sussex and London, and many other parts of the UK is typically above 300ppm. A photograph of the calcium in a sediment form can be viewed on Can you drink softened water? … it's easy to connect how the sediment can collect on the walls of the kidneys.

Myth or Reality – Are Kidney Stones Caused by Hard Water? also repeats the above.

Does drinking hard water lead to kidney stones? suggests "The impact of water hardness on urinary stone formation remains unclear, despite a weak correlation between water hardness and urinary calcium, magnesium, and citrate excretion. Several studies have shown no association between water hardness and the incidence of urinary stone formation. A correlation between water hardness and urinary calcium, citrate and magnesium levels has been observed although the significance of this is not known. Some studies suggest that in the preventive approach to calcium nephrolithiasis, intake of soft water is preferable to hard water since it is associated with a lower risk for recurrence of calcium stones. There is, however, no study as yet, which has shown a higher incidence of kidney stones in a population consuming hard water."

Does water prevent stones – what’s your bet? from the University of Chicago suggests that supersaturation causes crystals to form and grow, and states that people who make stones "supersaturate their urine excessively even if the actual measured values are no higher or even lower than those commonly found among normal people. The proof is that they make stones."