Modern sewer systems are typically designed to accommodate an average of 350 gallons per house per day with a peaking factor of three. The peaking factor accounts for the fact that everybody is flushing toilets and showering at 6:30am.
City budgets are in crisis with the melt down of the housing market for two reasons:
(1) The tens of thousands of dollars per new building permit are gone. In small cities, this is a ten million dollar annual hit.
(2) The reduction of housing value of 30% will eventually reduce the taxes from existing homes.
In order to save money, some Cities are stretching existing infrastructure by talking about reducing sewer design criteria to 220 gallons per house per day. This is the actual observed flow, and eliminates the safety factor. These cities assume that average household discharge will be the same in ten years as it is today.
But that is a bad assumption. The combination of waves of relatively low-IQ immigrants and a severe economic downturn will yield more people in each house. The average number could easily double.
That is why I think we can expect to see stories about sewer systems discharging into streets as our world moves forward. Border towns will be first.