As I said before, my gut feeling is that it probably is low. We're not solid on that number.
Part of it is the issue that you mentioned: do municipalities know where their pipes are? Even though they're solid pipes, there weren't records kept at the time, in most places, of what materials were used. Sometimes when houses are renovated, they change. Some places have a better handle on it than others; Halifax can speak to that.
Just using the expectations for the places that are focused on, it goes into the 200,000s—that's the number I have seen—but I expect it's larger. I don't know how much data there is. Graham may be more familiar with it.