What is the central claim of the passage?

A water bill pays for a fixed, aging system, and holding the price down only postpones a larger cost. (The claim is set in the second sentence and returned to at the end. The leaks and the ten percent are evidence for it, not the claim itself.)

According to the passage, what happens to a city's spending when it sells ten percent less water?

It stays much the same, because the costs do not move with use. (The passage answers this twice in a row: the pipes are just as long, and the plant runs anyway.)

In this passage, costs that are "fixed" are costs that

stay much the same whether much or little water is sold (Two sentences earlier the passage says almost none of that cost moves with the amount you use, and gives the ten percent example to prove it.)

What does the passage mean by "postponement charges interest"?

Putting off repairs makes the eventual cost larger. (The image is borrowed from lending: a debt left unpaid grows. Here the debt is maintenance, and the growth shows up as a fifth of the treated water leaking away.)

The Cost of a Cheap Glass: Level 4 Reading Comprehension Questions

A glass of tap water costs a household a fraction of a cent. That price is honest about the water and dishonest about everything else.

The water itself is free; it falls out of the sky. What a bill pays for is the watershed bought and protected, the reservoir and its dam, the treatment plant, the pumps, the tower, and the buried mains that carry pressure to every street. Almost none of that cost moves with the amount you use. A city that sells ten percent less water does not spend ten percent less. The pipes are just as long, and the plant runs anyway.

This is the awkward arithmetic of a network. The costs are fixed and enormous, the product is cheap and essential, and the customers vote. Raising the price of water is unpopular in a way that raising the price of almost nothing else is, so the price tends to stay where it was while the pipes age underneath it.

The bill for that arrives late, and in another form. In many systems a fifth or more of the treated water never reaches a tap, leaking out of joints laid before anyone now living was working. The cheap glass was never cheap. Its real price was paid in postponement, and postponement charges interest.

Comprehension questions