No it’s demonstrating that at the relative extreme ends you have the same problem thus creating the linear equation with the minimum set

The reader should deduce that any measure along the same linear map - which is effectively every city aka the “average city” - will eventually be subject to this condition (water insecurity)

You can trivially verify this by looking at issues of water insecurity and water quality issues across every size city. Notice that you will have non-trivial numbers of “boil water” events in the United States south. You may have significant periods of drought throughout your average city in sub-Saharan Africa, Sonoran desert or western China for example.

I think maybe your definition of “average” only includes modern metropolitan areas and not simply as cities where people are geographically clustering across the globe.

I lived in San Angelo Texas in 2009 and I did not have potable water in my home. I had to go to Walmart and fill 5 gallon jugs of Culligan water every few days. That’s not particularly abnormal

To be fair I offered a fairly complex/compressed way to approach this, so not easily interpreted, but nonetheless that’s the point