Milwaukee Remembers Cryptosporidium Outbreak of 1993

After deadly drinking water contamination a quarter of a century ago, Milwaukee now leads the field in water testing

Milwaukee Remembers Cryptosporidium Outbreak of 1993

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It’s every treatment plant’s worst nightmare: the people you serve getting sick from your plant’s water. The most potent example of this is the Milwaukee Cryptosporidium outbreak of 1993. Over 400,000 people were affected and more than 100 died.

Coming back from such a disaster takes fortitude and commitment — and for the city of Milwaukee, over $90 million in immediate treatment upgrades. To date, the city has spent $508 million in water infrastructure upgrades, not all related specifically to Cryptosporidium, but all in an effort to ensure their citizens are protected. 

The outbreak

This April marked 25 years since the infamous epidemic, which was likely the largest waterborne illness outbreak in U.S. history.

It took several days to identify the cause and source of the illness running rampant through Milwaukee, partially due to the lack of adequate testing facilities and an unfamiliarity with the contaminant.

A boil notice was issued for seven days, and they shut down the treatment plant that the Cryptosporidium had been linked to. The notice was only lifted after the plant had been thoroughly purged.

Recovering trust

Three main system upgrades took place in the immediate aftermath of the 1993 calamity. First was an $11 million project extending the plant intake out of the Milwaukee harbor and further into Lake Michigan, where most of its source water comes from. The harbor was believed to contribute a significant amount of contamination.

After that, they switched from a chlorine disinfection process to an ozone process, and did a full renovation of the treatment plant filter beds, switching to a dual-media system for biologically active filtration. The filter bed project cost $27 million, and the ozone retrofit was a $51 million endeavor.

In addition to physical changes, Milwaukee was forced to rethink many processes and organizational structures. To that end, first and foremost was the creation of a Water Quality Monitoring Program — the first line of defense against future outbreaks.

Moving forward

Today, Milwaukee uses state-of-the-art testing methods and facilities. According to the city’s website, the utility tests for more than 500 contaminants, while the EPA only requires testing for 91.

They have been a national leader not only in testing for microorganisms like Cryptosporidium, which actually wasn't required for source water testing until 2015, and were one of the first groups to start testing for endocrine-disrupting compounds (EDCs), pharmaceuticals and personal care products (PPCPs) in 2004.

Following the event, Milwaukee also increased cooperation between the Health Department and Water Works. Lack of communication between the departments was a factor in the city’s inability to diagnose the issue back in 1993.

The partnership is embodied by the Interagency Clean Water Advisory Council, which has promoted public health and raising awareness about growing threats to water quality since the ’90s.

“Water and public health, they may reside in separate jurisdictions within government, but they need to be connected and talk to each other,” said former Milwaukee health commissioner Paul Nannis in an article by “We need each other talking to each other so that we have the best of each world contributing to the solution.”


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