Although La Palma has more water than the other Canary Islands, many farmers used to be desperately poor and frequently hungry. The only water for irrigation was rainwater, and obviously they had no control over how much they got.
Then somebody suggested digging into the hillside to find water. (If anybody knows who, please tell me.) The idea is that much of the rainwater seeps into the ground, and runs through tiny cracks in the volcanic rocks for miles and miles before it comes out as a spring. (There are lots of springs where you can refill your water bottle on a hike, especially in the Caldera, which saves carrying so much water with you.) Much of it reaches sea-level underground, and is wasted. If you dig a tunnel horizontally into the hillside, you might well find an aquifer. Crucially, since the water takes anything up to fifty years to work its way through the ground, these galerías still run in a dry year.
It worked. In some places, this meant three harvest per a year instead of one, and the children weren’t hungry any more.
It was a tremendous amount of work, hacking away at the rock by candlelight with only hand tools and no idea of when, or even whether, you’d find water. But the prospect of a better life was enough to make people start, and keep going. Some are short, but the Pajarito galería is over 5 km long. I wonder how long that took?
These days, over half of La Palma’s water comes from the 170 galerías on the island. And very good water it is too.
Even better, you can help yourself. The local bottled water is so cheap that it’s not worth making a special trip, but my usual route to the Roque goes right past one of them. The water is channelled into a tank, and I refill old water bottles from the tap.
But it’s a bad idea to explore a galerías,especially on your own. There’s a danger of poisonous gases building up. Stick to the volcanic caves, like the one in Las Manchas.