Rain fell in Pittsburgh last week, and while that may be good news for gardeners, rainfall poses a problem for the city and region. While it is nasty to contemplate and nastier to encounter, when it rains around here -- even a small amount -- sewer systems often overflow into the rivers.

So on Thursday, the black and orange flags went up again along Allegheny County's rivers, indicating a combined sewer overflow day and our collective shame. It was the 10th alert of the recreational boating season.

This is a perennial occurrence. But unless you are out on the water, you might not know. The subject is not sexy, and it is not even polite. Worse, the solution is very expensive, a perfect storm of factors for those inclined to do nothing.

Yet the alarm has been sounded in numerous ways. A study released last year by the National Academy of Sciences -- sponsored by the Allegheny Conference on Community Development -- faulted 11 counties in southwestern Pennsylvania for having too many small, autonomous municipal treatment systems.

In 2002, a report called "Investing in Clean Water" by a committee of 60 business, government and civic leaders and the Pennsylvania Economy League outlined the problems that flow -- literally -- from the failure of the patchwork of municipal governments to keep the water clean. That same year, the Post-Gazette published a special series that revealed a grim litany of facts concerning water and sewer lines.

Even as the rains fell Thursday, a group of municipal leaders, managers and public works employees were in Cranberry discussing just these issues at the eighth annual 3 Rivers Wet Weather Sewer Conference. The previous day some 250 of them had heard Allegheny County Chief Executive Dan Onorato call for a cooperative effort to tackle the problem, offering to spearhead the effort, including lobbying for state and federal funds if the municipalities get their act together. Amen to that.

Keeping the water clean has to be done, not only because it's important to safeguarding public health -- and indeed economic development, as Mr. Onorato pointed out -- but because it is required by federal law. (Alcosan is currently negotiating with the Environmental Protection Agency on a consent decree to fix wet weather problems). The cost may be huge and the challenges great, but there is no choice.

Mr. Onorato gets it -- and we can only hope that other officials in the area get it too.