Q: The water we use for drinking at home is very rich in salt. We boil the water before drinking and find that the container is thickly coated with salt due to the regular boiling of water. Will consuming this salted water lead to kidney stones?

A:The hardness of water is due to the presence of carbonate & sulphate salts of calcium and magnesium. These minerals in hard water cause spots to form on dishes/cutlery and scale to form on plumbing and electric equipment like kettles and geysers. More than 3/4th of kidney stones are generally composed of calcium salt and usually occur as calcium oxalate and less commonly as calcium phosphate. The remaining 20% of stones are composed of uric acid, struvite and cystine stone. Stones form in urine that is supersaturated and this saturation is dependent on chemical free ion activity, which makes the urine become under-saturated. In this situation the stone will not grow and may even dissolve. Increased urinary ion excretion and decreased urine volume will both increase free ion activity and favour stone formation and growth. Formation of kidney stones (nephrolithiasis) is based on genetic, metabolic, nutritional and environmental factors. Metabolic factors involved in stone formation include hypercalciuria (found in 50% of patients and its most common cause is increased intestinal calcium absorption), hypocitraturia (due to renal disease), hyperuricosuria, hyperoxalaturia, cystinuria and infections. Environmental / nutritional factors include dehydration (e.g., exercise in hot climates), high salt intake, a diet rich in animal proteins and calcium rich diet when oxalate intake is restricted. 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.