A neighbour is coming towards me, labouring to carry 18 kg of bottled water (plus the weight of the bottles). He seems glad to stop, put the water down, pet the dog. I comment that he has enough water for a month. No, till this evening, he jokes. I tell him I’m very happy with Roman tap water. Oh no, it is very hard, he says, and causes kidney stones.
Every Italian, certainly every Roman, knows for a fact that hard water causes kidney stones. Maybe that’s why Italy leads Europe (and the world?) by drinking “136 litres of non-flavoured water per person per year”. Nagging doubts gnaw at me. Roman water does, after all, screw up just about any appliance that comes into contact with it. And if you had sat through Deadwood's amazing scenes of kidney stone distress, those doubts would gnaw at you too.1
To the internets, then, where three salient facts emerge.
While the amount may be a factor in the development of kidney stones, the hardness or softness of the water you drink is not.
There's even a suggestion that water with more calcium helps to prevent kidney stones, by encouraging the excretion of calcium.
If, however, you already have kidney stones, then drinking soft water can help to prevent their recurrence.
This has been a public service announcement.
2022-04-18: Italy is now (in 2019, that is) at 200 litres per person per year, way ahead of Germany at 168.