The cost of a plastic bottle

A plastic water bottle costs about five thousand dong. That price covers the plastic, the water, the transport and the shop's profit. It does not cover what happens next.

Most bottles are used once, for about fifteen minutes. After that, three things can happen. The bottle is collected and recycled, which uses energy but saves material. It is burned, which produces heat and air pollution. Or it is dropped, washed into a drain, and carried to a river and then the sea, where it breaks into pieces too small to collect.

Economists call the cost that nobody pays an externality. The buyer pays for the bottle; the river pays for the rest. One bottle is nothing. Vietnam uses billions a year.

Schools are an interesting place to change this, because the habit is formed here and the solution is boring. A refillable bottle and a working tap remove almost the whole problem. The difficulty is not technology; it is the ten seconds of inconvenience and the fact that nobody owns the tap.

Students at one school counted bottles in the yard for a week before and after installing two water stations. The number fell by two thirds. That is not a complete answer, and the measurement was rough, but it was their own number, collected by their own hands, and nobody could tell them it was invented.