In Part One, we explored the metrics that measure municipal water system health. Now we’ll analyze two case studies that demonstrate how poor infrastructure decisions can impact the health of residents who rely on their utilities to provide a safe water resource.
Waste Water to Potable Water – Cryptosporidium
Spring came late to Milwaukee, WI in 1993. Frozen ground remained snow covered until late March when sudden high temps and heavy rains resulted in a rapid melt and runoff. Through creeks, streams, and rivers, the melt water from within the city as well as outlying agricultural land drained into Lake Michigan where prevailing winds blowing back towards the city pushed the new runoff towards shore and the city’s potable water intakes. As the official story goes, it was the agricultural runoff, combined with a perfect storm of wind and sudden thaw, that carried cysts of cryptosporidium into the city’s water supply.
The crypto parasite is a resilient pest whose outer membrane or shell allow it to survive for long periods without a host. Once consumed by humans, symptoms of cryptosporidiosis generally begin after 2 to 10 days. That brief incubation period was long enough for the parasite to go unnoticed in Milwaukee until over 400,000 people were infected, representing the largest outbreak of waterborne disease in American history. Officially, no deaths resulted, but later research suggests that an estimated 100 early HIV related deaths occurred at least in part because of the outbreak.
Later studies, specifically genomic testing of the cryptosporidium parasites present in Milwaukee in
1993, have determined that livestock were not the source of the outbreak. The Milwaukee crypto had a human source. An unthinkable infrastructure factor led to contamination of the potable water supply by human waste. Milwaukee, like many older cities, operates a combined storm and sanitary sewer system. That means that rainwater and wastewater are treated together. This is fine until there is a major storm event that overwhelms the system. At that point, Milwaukee releases combined sewer overflow into Lake Michigan. That means untreated human waste is released into the same body of water from which the city’s drinking water is sourced. It’s a big lake, but… not cool. And this issue is not unique to Milwaukee. Many older cities along the Great Lakes have identical systems in place.
Fortunately, this disaster led to more stringent guidelines for crypto testing in cities across the country. Unfortunately, the practice that led to this outbreak has not ceased. In 2018, Milwaukee’s combined sewer system overflow totaled 1.3 billion gallons.
Inadequate Treatment – Legionella
I’m going to talk about Flint, but I’m not going to discuss lead poisoning just yet. That will happen in Part Three when I analyze piping materials, as lead service lines are present all over this country. Instead, I’m going to focus on the 87 Flint residents who were stricken with Legionaires disease, 12 of whom died, during the same water crisis brought on by switching the city’s water source from Lake Huron via Detroit Water and Sewerage Department to the Flint River.
The presence of Legionella bacteria in municipal water pipelines is not unique to Flint and is probably not uncommon at all in cities across the country. Fortunately, water utilities have developed methods of water disinfection downstream of treatment plants, typically involving chlorine, chloramine, or other chlorine compounds. These chemicals have to be added to water in just the right ammounts: too little won’t effectively disinfect the water, and too much can be harmful when consumed. So how do utilities know how much chlorine they need to add?
Perhaps the most important factor in determining the degree to which a utility’s water must be chlorinated is the “chlorine demand” of the raw water being treated. When chlorine based disenfectants are introduced into a water source, some chlorine will react with the organic material, metals, and other compounds contained in the water and will no longer function as a disinfectant. Chlorine demand is not only unique to the particular makeup of a water source, but in the case of surface water (lakes and rivers), weather events hundreds of miles from a city’s water treatment plants can influence chlorine demand.
Whatever disinfectant is left over after the water’s chlorine demand has been met is called “free chlorine” and effectively inactivates (kills) disease causing organisms. As free chlorine makes its way down water mains and services, it is “used up” as it neutralizes parasites, viruses, and bacteria. Any chlorine left over coming out of a faucet in your home is called “residual chlorine.” The WHO has determined that residual chlorine levels of at least 0.5 mg/liter at a water line’s endpoint will be effective in killing the nasties. According to the CDC, water with residual chlorine levels under 4 mg/liter is considered safe for consumption, so treatment operators are aiming for a window between 0.5 and 4 mg/liter in order to protect their rate payers from disease without poisoning them.
Sourcing water from the Flint River changed the chlorine demand of the city’s water, as did the presence of lead and other heavy metals in the water system. Not adequately accounting for this change meant that residual chlorine levels were too low to inactivate Leagionela bacteria present in the biofilm of aging metallic mains and services.
This chart shows that parasitic and chemical associated outbreaks have been on the decline in this country since the early 80’s, likely due to the adoption of more stringent regulation mandating tighter standards and more rigorous testing, with Milwaukee’s crypto outbreak being the most significant catalyst for change. But look at the black blob in the lower right-hand corner. Legionella outbreaks are on the rise thanks to an increased presence of biofilm in our ageing water infrastructure.
As long as the residual chlorine levels coming out of every tap in the city, no matter the distance from a treatment plant, are 0.5 mg/liter or higher, we’ll all be fine. But isn’t adjusting the level of disinfectant to match the demand of fluctuating water quality, while being careful not to add too much chlorine lest you harm your citizens with the product that should protect them, a dangerous proposition? Wouldn’t it be easier to manage a water system where bacteria harboring biofilm isn’t present?
Seems like common sense. So is not shitting where you eat (or drink).
Stay tuned for Part Three where we’ll explore materials-based solutions to these problems.