Where I live (Albany, NY) "fixing" the sweet systems in our country, which is a shared storm/sanitary system built in the early 19th century by burying existing streams, would cost something like $4 billion. The money just isn't there for a county with 300,000 people to fund huge capital projects like that.
As a result, everytime we get a heavy rain, we are dumping raw sewage into the Hudson River.
IMO, the Federal government should buy a few less F-35s and find projects like this -- valuable public works that will employ people and benefit society for 100 years or more.
Combined sewer overflow [1] is essentially business as usual in many municipalities. I happened to learn about the Detroit sewer system, but even King Co in the PNW has this issue [2]. I like to think areas like that would think ahead about this, given the high annual rainfall, but separate systems are quite the expense.
[1]: https://en.wikipedia.org/wiki/Combined_sewer#Combined_sewer_... [2]: http://www.kingcounty.gov/healthservices/health/ehs/toxic/cs...