Instead, seepage will "simply" be worse, or accelerated more, than before the "additives."
As the seepage becomes leaks and washes out the foundations of roads, in most cases, the city streets will show it. I suspect that the level of this, being a surprise to the public, will happen sometime over the next three years.
There is already some good bypass gear (plastic pipes and valves) available, but not on the scale that I expect we will need. And, in the northern climates, especially north of the 40th parallel, the bypass gear will probably be set up and remain until the weather improves.
Some logistical preparation, based upon known ages of water lines, might already be long overdue.
You might suggest, as silly as it seems, that some civil engineers try to keep data on the sales of toilet bowl gaskets, flush-valve seats in particular. If sales are significantly up where new home development cannot account for it, that might show the caustic effects of the newly, post-9-11, treated municipal water supplies.