April 25, 2014. In a money saving maneuver, the city of Flint, Michiganunder the authority of a state appointed Emergency Managerswitched its municipal water supply from Lake Huron to the Flint River. This switch would trigger a chemical chain reaction with devastating results: thousands of children exposed to lead poisoning, and very likely two outbreaks of Legionnaires Disease, claiming twelve lives.

Narrated by Joe Morton (“Scandal”), PBS’ documentary “Poisoned Water” – produced under its NOVA science banner – will investigate the well documented Flint, MI water crisis, asking the broader question of how safe are tap water is. “Poisoned Water” uses the lens of science to reveal how the water disaster in Flint has brought to light a disturbing truth about the vulnerabilities of water systems across the country.

An eye-opening account, the documentary investigates exactly what went wrong in Flintfrom the delicate intricacies of water chemistry, to the biology of lead poisoning, to the misuse of science itself.

“Poisoned Water” premieres tonight, Wednesday, May 31, 2017 at 9PM ET/8C (check local listings).

The water crisis in Flint has affected thousands of people, and we now know that many cities around the country are vulnerable, said Paula S. Apsell, Senior Executive Producer, NOVA. If were going to tackle these problems, we have to understand why theyre happening. POISONED WATER explains the science the chemistry, biology and engineering that lies at the heart of this story.

Guided by the nations leading water experts and with intimate access to families most affected by the crisis, “Poisoned Water” will unfold like a detective story, from the first signs of trouble that came in the form of discolored water, to an increase in reports of skin rashes and hair loss, complaints from worried citizens, State officials insisting the water was fine, indications that it clearly was not, to the aftermath and resulting uproar.

Flint mom LeeAnne Walters was among the first to suspect something seriously wrong, spurred on by the living experiment she had in her own home: her twin boys. One of them wasnt growing properly.

Walters was connected with Miguel Del Toral, part of the EPA Region 5, who became concerned about Flints water treatment after hearing about a series of problems in the system. He wrote a preliminary report on the situation in Flint and shared it with Walters, who gave it to the press.

Unwilling to accept the citys response that the water was drinkable, Walters took matters into her own hands, contacting an independent research team from Virginia Tech, headed by chemical engineer Marc Edwards. Testing the tap water in Walters home, Edwards was stunned by the results: not only was there lead in the water, but the levels were so high that the water flowing from her homes faucets qualified as hazardous waste.

“Poisoned Water” follows the trail of evidence as Edwards and his Virginia Tech team, including civil engineer Siddhartha Roy, leapt into action investigating exactly what had gone wrong when the local authorities switched the city water supply. To solve the mystery, the researchers would need to unravel the complex chemistry that played out in the water pipes running beneath Flints streets and inside its residents homes.

The crisis in Flint, a poverty-stricken and predominantly African American community, is just one striking example of how science intersects with social justice. Edwards had seen this kind of chemical disaster before. On NOVA, he and former EPA environmental engineer Elin Betanzo recount the story of the water contamination crisis that unfolded in Washington, DC in the early 2000s. There, the water authority switched the chemicals used to kill bacteria in the water supply. What they didnt realize was that the new water chemistry would strip the protective coating inside the pipes, corroding the metal, leaching lead into the water system and exposing thousands of people to lead poisoningincluding, it is suspected, members of Congress.

As Edwards and other water engineers explain, both the DC and the Flint crises could have been avoided if authorities had carefully managed the water chemistry. NOVA reveals the discovery that the Flint water authority failed to add a key chemical, called a corrosion inhibitor, which can help pipes build up a healthy scale to protect them from corroding. Drinking the water from Flint pipes was like drinking through a lead-painted straw.

When Edwards heard from Walters in 2015, he had a strong suspicion that, just like in DC over a decade earlier, the water utility was hiding something. But because of his experience with the DC water crisis, he was undeterred; he had a plan. His team coordinated its own widespread testing of Flints water.

When they analyze the results, Edwardss suspicions are confirmed. It is undeniable. Flints municipal water system is contaminated with lead, exposing thousands of children to the risk of lifelong intellectual deficits and behavioral problems. Evidence of the danger to children is revealed after Betanzo persuades her friend Dr. Mona Hanna-Attishaa pediatrician with access to crucial blood data at Flints Hurley Childrens Hospitalto conduct a study to determine whether the lead levels in childrens blood have increased in the period before the change from the Detroit water system to after the switch to the Flint River water source.

However, as “Poisoned Water” exposes, the disaster did not stop there. One last deadly secret emerged: there had been two outbreaks of Legionnaires disease in Flint which were not reported until well after they occurred. Twelve people died. NOVA visits the lab bench of Amy Pruden, who along with Marc Edwards suspects that the growth of Legionella–the bacteria responsible for Legionnaires disease– was in fact also connected to the lack of corrosion control.

In Flint, the city has switched back to Detroit water after enormous public pressure, but the damage to the pipes has been done. A residential pipe replacement project has begun as part of the solution. The job will not be easy, it will not be cheap, and it will not be quick.

Whats moreoverhauling Flints failing water infrastructure is only a microcosm of the gargantuan task of fixing Americas drinking water infrastructure, something to which the American Society of Civil Engineers gives a grade of a D.

Meanwhile, fearful Flint residents are still living off bottled water. With their trust of the government as corroded as the pipes themselves, some have resigned themselves to it for a lifetime.

“Poisoned Water” is a NOVA production by BlueSpark Collaborative, LLC for WGBH Boston. Written and directed by Llewellyn Smith. Produced by Llewellyn Smith and Kelly Thomson. Executive Producer is Julia Cort. Senior Executive Producer for NOVA is Paula S. Apsell.

National corporate funding for NOVA is provided by 23andMe. Major funding for NOVA is provided by the David H. Koch Fund for Science, the Corporation for Public Broadcasting and public television viewers. Additional funding is provided by the George D. Smith Fund and the Millicent and Eugene Bell Foundation.