As I commented on their own comments section:

The only graphic in this article is "city shrinkage", which is then conflated with water age, which is then related to water problems. But I suspect these things may not be as linearly connected as the authors imply, specifically because of factors like the chemistry of incoming water, as exemplified by the Flint situation.

Also, water systems can have vastly different flow rates, pipe sizes, and other parameters that influence water age, not just population change.

So, is there better data? Can we actually show a relation between city shrinkage, water age, and water problems? If this data exists, why wasn't it presented? If this data doesn't exist, why is a relationship suggested?