Comment by lisper

> the water in the tank was so pure it had dissolved a spanner/wrench that was left in the bottom

"Apparently somebody had left a wrench there when they filled it in 1995," he said. "When they drained it in 2000 the wrench had dissolved."

I dunno, I think if you left a wrench soaking in regular water for five years there wouldn't be much left of it after that either.