The Flint water crisis was caused by a decision to switch the city’s water supply from Lake Huron to the Flint River on April 25, 2014, combined with a critical failure to treat that new water for corrosion. Without the right chemical treatment, the river water ate away at protective coatings inside Flint’s aging lead pipes, sending dangerous levels of lead into the drinking water of roughly 100,000 residents.
The Water Source Switch
For decades, Flint purchased treated water from Detroit’s system, which drew from Lake Huron. But Flint was under state-appointed emergency management, and city officials were looking to cut costs. In 2013, they decided to join the newly formed Karegnondi Water Authority, which was building its own pipeline from Lake Huron. That pipeline wouldn’t be ready for about two years.
Rather than negotiate a short-term contract with Detroit to bridge the gap, Flint officials chose to draw water from the Flint River and treat it at the city’s own plant. The switch happened on April 25, 2014. Almost immediately, residents began complaining about the water’s color, taste, and smell. Those complaints were early signals of a much deeper problem.
The Missing Corrosion Treatment
The single most important technical failure was the decision not to add a corrosion inhibitor to the new water supply. When Flint was receiving Detroit water, that water contained orthophosphate, a chemical additive that forms a thin, protective mineral layer on the inside of pipes. This coating acts like a seal, keeping lead and other metals locked in the pipe walls and out of the water.
When Flint switched to river water, no one continued dosing orthophosphate. Testing confirmed that phosphate levels in the water dropped to zero after December 2014. Without that protective layer being maintained, the mineral scale that had built up inside pipes over decades began to break down. Lead dissolved and flaked off directly into the water flowing to people’s taps.
The Flint River also had higher chloride levels than Lake Huron, which made the water more chemically aggressive toward metal pipes. Chloride concentrations in the river were significantly elevated, particularly downstream of industrial and municipal discharge points. This corrosive water, flowing through unprotected lead service lines, created the perfect conditions for widespread lead contamination.
Lead Exposure in Children
The health consequences showed up quickly, especially in children. A study published in the American Journal of Public Health found that the percentage of Flint children with elevated blood lead levels doubled after the water switch, rising from 2.4% to 4.9%. In neighborhoods where water lead levels were highest, the increase reached 6.6%.
For context, children outside Flint had an elevated blood lead rate of just 0.7% during the same period, and that number didn’t change. The disparity made clear that something specific to Flint’s water was driving the spike. Lead exposure in young children is particularly harmful because it can cause lasting damage to brain development, affecting learning, behavior, and attention even at low levels. There is no safe level of lead in a child’s blood.
Legionnaires’ Disease Outbreak
Lead wasn’t the only danger. During the crisis, 86 residents of Genesee County developed Legionnaires’ disease, a severe form of pneumonia caused by bacteria that thrive in warm water systems. Changes in water chemistry, particularly reduced chlorine effectiveness in the more organically rich river water, likely created conditions for Legionella bacteria to grow in the city’s distribution system and in building water systems like cooling towers. The outbreak was one of the largest associated with a municipal water supply in U.S. history.
Regulatory Failures at Every Level
The crisis wasn’t just a technical mistake. It was enabled by failures in oversight at the state and federal level. The Michigan Department of Environmental Quality was responsible for ensuring Flint’s water met federal standards under the Lead and Copper Rule. That rule requires water systems to monitor lead levels and implement corrosion control treatment. State regulators did not require Flint to add corrosion control when it switched water sources.
Testing practices made the problem harder to detect. Sampling methods used in Flint, including bottles that restricted water flow and instructions to flush pipes before collecting samples, could minimize the lead readings that showed up in official results. The EPA has acknowledged that water utilities across the country have collected samples in ways that can miss high lead levels. In Flint, biased selection of sampling sites further obscured the true scope of contamination.
The Lead and Copper Rule itself had structural weaknesses. Its action level for lead is based on what’s technically feasible to control, not on health-based thresholds. First-draw sampling protocols don’t capture water that has been sitting in the lead service line itself, meaning the most contaminated water can go untested. These gaps allowed problems to persist for over a year before the full extent of the crisis became undeniable.
Warning Signs That Were Ignored
There were clear signals well before the crisis became national news. Residents reported discolored, foul-smelling water within weeks of the switch. By October 2014, General Motors had stopped using Flint River water at its local engine plant because the water’s high chloride content was corroding engine parts. If the water was too corrosive for car manufacturing, it was certainly too corrosive for lead pipes delivering drinking water to homes.
Independent researchers, particularly a team from Virginia Tech led by Marc Edwards, began testing Flint’s water in 2015 and found lead levels far exceeding federal limits. A local pediatrician, Dr. Mona Hanna-Attisha, published the blood lead data showing the spike in children. State officials initially dismissed both sets of findings before eventually acknowledging the crisis in October 2015, more than 17 months after the switch.
Pipe Replacement and Current Water Quality
Flint reconnected to Detroit’s Lake Huron water supply in October 2015, and corrosion control treatment was restored. But the damage to the city’s pipe infrastructure meant that simply switching back wasn’t enough. Nearly 11,000 lead service lines were identified for replacement under a court agreement, and by July 2025, the final lines in that agreement had been replaced. Roughly 98% of residential lead service lines in the city are now gone, with work continuing on remaining lines that homeowners had previously opted out of or that were discovered during later inventory.
Water quality has improved dramatically. In the first half of 2024, Flint’s 90th percentile lead level measured just 1 part per billion, meaning 90% of tested homes had lead at or below that level. The federal action level is 15 parts per billion. Flint has now been in compliance with Michigan’s lead standards for nine consecutive years.
Legal and Financial Fallout
The crisis triggered years of litigation. In one of the largest settlements, approximately 26,000 individual plaintiffs, including a significant number of children, received compensation. In February 2025, Veolia North America, the engineering firm that had been hired to advise on Flint’s water treatment, agreed to pay $53 million to settle claims from affected residents. Multiple state officials faced criminal charges, though many of those cases were later dropped or remain unresolved.
The total financial cost of the crisis extends far beyond legal settlements. It includes pipe replacement, medical monitoring for exposed children, lost property values, and a deep erosion of public trust in government institutions. For a city that was already struggling economically, the crisis compounded existing hardships in ways that will take generations to fully measure.