So often any of these single causal theories forget to look at timespan. Which was either decades or centuries... If system survived previously with mostly same things in place there is really no reason why such thing as lead pipes would be the cause of downfall part. By any reasonable conclusion the culprit in such case should be some disruptive innovation. In the end gradual natural degradation of system is much mo…
Complex systems fail due to single causes exactly that way. First the system runs well; once the cause is introduced the system adapts so that the visible cost is minimal, but the adaptations are costly by themselves, and demand further adaptations; then the adaptation cycle runs for a while (that can be very long), until everything finally breaks down. It is very unlikely that the lead pipes that were there since th…
You can use a caustic solution to unclog your pipes and it will work flawlessly, every time for an indefinite amount of time. Then, at some point, you'll have leaks due to glue being eaten away, PVC melting, or other damage.