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In Laos today, there is a widespread perception that 'nam hin boun' (hard water), specifically water that contains dissolved calcium, causes the formation of kidney stones. This belief is prevalent among nearly all sections of society including medical and professional workers.  

In fact, international medical research has shown that just the opposite is the case.  'Nam hinboun' actually helps prevent the formation of kidney stones as well as many other harmful diseases. 

"Benefits of adequate [Nam Hinboun] intake are noted in bone health (i.e. prevention of osteoporosis and rickets), decreased likelihood of kidney stone formation, less hypertension and stroke, and decreased insulin resistance.  In settings of low calcium intake, the risk of these diseases, as well as colorectal cancer, cardiovascular disease, and obesity, increases. Thus, there is benefit to dietary calcium and risk if it is deficient.  Since most people, especially in developing nations, consume a diet that is low in calcium, the WHO reasonably concludes that hard water will provide benefit rather than harm.

Regarding kidney stones, dietary calcium (especially that consumed with food and water) reduces the incidence of stones.  Calcium binds oxalate in the small intestine so that oxalate is less absorbed, thus promoting a decrease in oxalate stone formation (oxalate stones are the most common type of kidney stone).  Thus, the WHO reasonably concludes that [nam hinboun] not only poses no risk of kidney stones to populations at large, but it may actually help prevent the formation of kidney stones."

Get the full paper here in English or here in Lao language