One morning in the small Transylvanian mountain resort of Baile Homorod, in Romania, travelers and residents gathered under the shade of a wooden canopy near three streams of sparkling spring water to fill up a row of empty bottles.

This is no ordinary water.

It flows from volcanic mountains nearby and pours into the springs here. At its best, it’s cool, clear and prickly, with a rich taste of minerals. At its worst, it can quickly develop a foul smell and stain everything in sight a dark amber. But residents swear by its curative powers.

Balint Vencel, 36, a frequent visitor, says the water helps with his kidney issues.

“I’ve seen doctors and they didn’t help,” he said. “But ever since I’ve been drinking this water, I haven’t had any pain in my kidneys.”