Three weeks ago, the state received reports of high levels of contaminants in a 70-mile stretch of the Monongahela River. There were no reports of illness and tests did not show the water to be unsafe.

But since 325,000 people get their water from this part of the Mon, the Department of Environmental Protection recommended the use of bottled water for customers of 11 public water suppliers, particularly those whose tap water smelled foul and tasted bad.

The culprit was TDS -- total dissolved solids -- which can enter a river from abandoned mines, agricultural runoff, wastewater from gas drilling or discharges from industrial or sewage plants. Last week, the Army Corps of Engineers began a release of additional river water through dams to dilute the TDS levels.

Such alerts and precautions in Western Pennsylvania are not unusual, and each incident highlights the precarious state of clean water in a region with so much industry and aging infrastructure.

Many of the old water and sewage treatment plants are no longer able to do the job. Federal monitors reported years ago that the region's systems needed a costly overhaul if public health was to be protected and compliance with the Clean Water Act was to be ensured. The price tag for that was a projected $3 billion.

Gov. Ed Rendell said that statewide the problem will cost nearly $20 billion to address over the next 10 to 15 years, with customers of individual treatment systems unable to bear the load. That's why Pennsylvania voters will be asked a ballot question next Tuesday -- whether the state should float $400 million in bonds to investors that would generate grants and low-interest loans for the repair of local water and sewer systems.

We strongly recommend a Yes vote, not because the bond proceeds will take care of the whole problem, but because they will make an important start toward addressing a fundamental need: clean, safe drinking water.

As to whether this is a good time for the state to borrow money, given the drop in revenue collections and the economy's instability, voters can take comfort that Wall Street credit rating agencies rank Pennsylvania as a low-debt state. Debt service accounts for only 3.5 percent of General Fund revenues, and the three major agencies -- Moody's, Standard & Poor's and Fitch -- give the commonwealth a double-A rating.

Unfortunately, more dollars beyond this bond issue will be necessary to complete the modernization of Pennsylvania's treatment systems. But the magnitude of the crisis should not paralyze the public into inaction. Approving Tuesday's referendum is needed to keep the effort flowing.