Water at Scale. Four generations of plumbing, all buried.

Rome piped water in. The nineteenth century added sewers. The twentieth added filtration and chlorine. The twenty-first has to add reuse, because the easy rivers are already taken. Each upgrade was invisible to the people it saved, which is why water engineering is argued about in generations rather than budgets.

• Filtered, chlorinated supply produced one of the largest jumps in urban life expectancy ever recorded. The pipes are underground, so the credit usually goes somewhere else.
• A dam does not create water. It moves water in time and in space, and somebody downstream always notices. Most water disputes are arguments about who is downstream.