I went to hear some missionaries report on their activities in a far-off tropical country. It was all the usual stuff until they started to describe their homebuilding efforts. In a village that consisted solely of grass-huts, they erected a western-style bungalow. And whereas the rest of the village went to the toilet in the nearby mangroves, they installed a toilet inside their bungalow — complete with septic tank. The septic tank was a bone of contention with the villagers who claimed it would contaminate their water and make them all ill. Our missionaries dismissed this as ignorant superstition.

In fact the villagers were right and it was the missionaries who were ignorant. The village was located on a very flat sandy island and its wells tapped into a ‘freshwater lens’. Now the effluent from their septic tank was emptying into that same water lens — and everybody (including our missionaries) became sick.