Flint’s water became dangerous in 2014 when the city switched its water source from Lake Huron to the Flint River without adding a critical chemical that prevents lead from leaching out of old pipes. That single decision exposed roughly 100,000 residents to lead-contaminated drinking water, triggered a Legionnaires’ disease outbreak that killed 12 people, and created one of the worst public health emergencies in modern American history.
What Went Wrong With the Water
For decades, Flint’s water came from Lake Huron through the Detroit water system. That water was treated with orthophosphate, a compound that coats the inside of lead pipes and forms a protective mineral layer. This layer, called scale, acts as a barrier between the lead in the pipe walls and the water flowing through them. Over time, this coating builds up and keeps lead levels low.
In April 2014, Flint switched to the Flint River as a cost-saving measure. The new water was not treated with orthophosphate. Without that protective coating, the river water began eating away at the mineral scale inside Flint’s aging lead service lines. As the scale broke down, it released both the lead from the pipes and the old phosphate deposits that had trapped lead particles for years. Researchers tracking two Flint homes found an extremely strong correlation between lead and phosphate levels in flushed water samples, confirming that the old protective layer was literally dissolving into the drinking supply.
The Flint River water was also more corrosive than Lake Huron water, which accelerated the damage. The city had tens of thousands of lead service lines connecting water mains to homes, some more than 50 years old. Every one of them became a potential source of contamination.
Lead Was Not the Only Problem
The corrosive river water also reacted with iron pipes in the distribution system, consuming the chlorine that was supposed to disinfect the water. With chlorine levels dropping, bacteria thrived. An outbreak of Legionnaires’ disease struck Genesee County (which includes Flint) in 2014 and 2015, sickening 86 residents and killing 12. Researchers eventually linked about 80% of those cases to the decline in chlorine caused by iron corrosion in the water system.
On top of that, the water treatment plant struggled to control disinfection byproducts called trihalomethanes, which form when chlorine reacts with organic matter in the water. The federal safety limit is 80 micrograms per liter. Some sampling locations in Flint hit 162, 181, and even 196 micrograms per liter in the summer of 2014, more than double the legal maximum. Long-term exposure to trihalomethanes is associated with increased cancer risk and liver and kidney damage. The city received a formal violation of the Safe Drinking Water Act for these levels in December 2014.
How Lead Harms the Body
There is no safe level of lead exposure. Children are especially vulnerable because their developing brains and bodies absorb lead more readily than adults. Lead exposure in children causes damage to the brain and nervous system, slowed growth, learning and behavior problems, and hearing and speech difficulties. These effects translate into lower IQ scores, reduced ability to pay attention, and underperformance in school. There is also evidence that childhood lead exposure causes long-term harm that persists into adulthood.
Adults face a different set of risks. Even relatively low blood lead levels (below 10 micrograms per deciliter) are associated with increased blood pressure and a higher risk of hypertension. Levels below 5 micrograms per deciliter, which is quite low, are linked to decreased kidney function and increased risk of chronic kidney disease. Lead also affects reproductive health: in men, it can decrease sperm counts and increase abnormal sperm. In women, blood lead levels below 10 micrograms per deciliter are associated with adverse reproductive effects, and higher levels are linked to delayed conception.
Why the City Didn’t Act Sooner
Residents began complaining almost immediately after the switch. The water looked discolored, smelled odd, and tasted wrong. State and local officials repeatedly assured the public the water was safe. It took more than a year, and independent testing by researchers at Virginia Tech and a local pediatrician who documented rising blood lead levels in Flint children, before the state acknowledged the crisis in October 2015. The city finally reconnected to the Lake Huron water supply and resumed corrosion control treatment, but the damage to the pipes, and to public trust, was already done.
Where Flint’s Water Stands Now
Flint’s water has been in compliance with federal and state lead standards since July 2016. The most recent testing period, covering the second half of 2025, showed a 90th percentile lead level of 6 parts per billion. That is well below the federal action level of 15 ppb and also below Michigan’s stricter 12 ppb standard, which took effect in 2025. These samples were drawn specifically from homes and businesses known to still have lead service lines, making them a conservative measure of the city’s water quality.
About 98% of residential lead service lines in Flint have been replaced. Roughly 500 lines still need work, either because homeowners previously opted out of the replacement program or because the lines were discovered during a citywide inventory completed in late 2024. The city and state continue working to replace those remaining pipes. While the water now meets safety standards, the crisis left lasting health consequences for residents who were exposed, particularly children whose developmental years overlapped with the contamination period.