Twenty-five years ago, an estimated 400,000 people fell ill and at least 69 people died in one of the most deadly waterborne-disease outbreaks in U.S. history. The outbreak had lasting effects nationwide, including in Portland, where the Portland Water District exemplifies the lessons learned: While our source water is pristine, we are proactive in protection and monitoring to keep it that way.

This month marks the 25th anniversary of the Milwaukee, Wisconsin, outbreak of Cryptosporidium, a parasite that can be found on surfaces or in soil, food or water that has been contaminated with the feces from infected humans or animals.

So what happened in April 1993? Deep snow that had built up over the winter was all released into the watershed during a spring rainstorm. The wastewater plant was overloaded, and combined sewer overflows poured into Lake Michigan.

The discharge from the plant and the sewer overflows flowed over the intake to one of Milwaukee’s two drinking-water treatment plants. Because Cryptosporidium is resistant to chlorine, the pathogen was unaffected by the plant’s disinfectant. Then, the filtration plant failed to remove the microorganisms and the pathogen entered the drinking-water system.

Customers started to complain of dirty, smelly water. Symptoms begin to appear two to 10 days after ingestion, so many people seen were out of work and school with gastrointestinal illnesses. Pharmacies couldn’t keep Imodium in stock. City and state health agencies oncluded that the drinking water was the likely source of the illness. After the state epidemiologist said he would not drink Milwaukee water, the plant was shut down and a citywide boil-water advisory was issued.

In the years that followed, Milwaukee Water Works increased water-quality monitoring and improved the automated system that reports on and controls the treatment plants. Drinking-water treatment processes and wastewater systems were upgraded, including the use of deep-tunnel storage of overflow stormwater. Parks, greenways and other natural areas were put in place to absorb stormwater runoff, and the utility hired its first water quality manager – me – to help get things back on track.

The outbreak was a huge wake-up call, solidifying the drinking-water industry’s understanding that we are in the business of protecting public health, not just treating and distributing water. We began to view operators as skilled positions and realized the importance of maintaining and reinvesting in our infrastructure. The importance of multiple barriers to prevent contamination came into focus. We also learned that regulations need to be considered in relation to each other, not in isolation, and optimal performance of wastewater systems is essential. New federal rules addressed the health effects of Cryptosporidium in surface water used as a drinking water supply.

Here at the Portland Water District, one of the most significant efforts resulting from the Cryptosporidium crisis was the installation of an ultraviolet water-treatment barrier in 2014 to comply with new regulations. UV treatment offers further protection from contamination and has been shown to enhance water quality throughout the distribution system.

Sebago Lake, the source of our drinking water, is so clean that the water district has an exemption from filtration. Our aggressive watershed protection program involves multiple activities: water quality monitoring, lake security, property inspections, erosion control and pollution prevention actions, environmental education and outreach, and land acquisition and conservation.

Another significant change involves the widespread use of data to guide adjustments that better protect public health and the environment. Before the Milwaukee outbreak, water testing and use of water quality data were largely the responsibility of the laboratory. The lab analyzed; operations operated.

In the late 1990s, the Portland Water District began an effort to “make water quality everyone’s business.” Now, years later, there is a much greater understanding of regulatory and water quality information throughout the organization. And scientists have a better understanding of the operational issues and practices that can influence water quality.

We have interdisciplinary teams that review data and act on results, and we have strong connections with the public health community. We have qualified and dedicated staff in place to operate and maintain an effective multiple-barrier treatment process. We understand that optimal performance of wastewater systems is critical to the health of our environment, and we continue to invest in improvements.

As the water district’s general manager of just over a year, I am immensely impressed with this organization and the dedicated workforce. They work every day, serving our community, protecting public health and the environment.