It is possible to trace every drop of toxic water spewed from Flint, Michigan back to two terrible decisions. The second was switching the city's supply from treated Lake Huron water to the corrosive broth in the Flint River. Left untreated, that water unleashed the disaster stored in the walls of the city's first bad decision: its lead pipes.

In the past few weeks, the nation's attention has increasingly focused on Flint's public health disaster. At least 15 percent of the city's homes have water with lead levels exceeding the safe limit established by the federal government. Several of those homes had water with lead levels 900 times above the safe limit. Poor political decisions caused the crisis, but it wouldn't have happened at all if the lead pipes weren't there to begin with. The current solution is a stopgap—spiking the water supply with an anticorrosive chemical. But if the powers that be want to eliminate the risk completely, they will ultimately have to replace all the lead plumbing. A September estimate, only recently released by Michigan governor Rick Snyder, puts the cost of replacing all the lead pipes in Flint at $60 million. And the project will take 15 years.

The basic challenge: dig up several thousand miles of poisonous pipe buried as deep as dead bodies.

Oh, for Pete's sake. People can only take bottled water baths for so long. "I don't understand, are they only going to fix four pipes a day?" says Harold Harrington, business manager of Flint's plumber's union, the United Association Local 370. He says with the right kind of investment, the city—or state, or whoever ends up taking responsibility—could move a lot faster.

Most of the corroded pipes in Flint—20,000 to 25,000 in total—are what is known as service lines. These are one inch in diameter, and connect homes to the larger, main pipes running under the middles of streets. (The mains are cast iron.) Because Flint is in Michigan, and Michigan is a very cold place, the service lines have to be buried about three and a half feet deep, below the frost line. "But most of the main pipes are between five to seven feet deep, so the service lines are at a similar depth," says Martin Kaufman, a geographer at the University of Michigan-Flint. So that's the basic challenge: dig up several hundred miles of poisonous pipe buried as deep as dead bodies.

Before calling in the backhoes, somebody needs to figure out where all those pipes are buried. Not just which houses they’re in, either. Remember, the pipes are an inch wide, and buried under roads, sidewalks, and front lawns, beneath lattices of cables, fiber optic wires, and gas lines. Digging in the wrong place would be both dangerous and expensive. Kaufman is one of those in charge of figuring out where all the lead pipes are buried, but the pipelayers of yore didn't do him many favors. "The recordkeeping of the city is not very good," he says. "They kept information on three by five index cards, a lot of which are smeared." The only definite way to check if a pipe is lead or not is to scrape the pipe's interior as it comes into the house. "If the residue is gray and nonmagnetic, it is lead," he says.

Let's say Kaufman and his peers deliver a city-wide lead pipe map to Harrington and his brothers and sisters in the United Association of Plumbers and Pipefitters. The check is blank, the backhoes are fueled up, and an army of plumbers stands at the ready: How long would it take to re-plumb Flint?

Replacing a typical service line takes three people. "You need an operator to run the equipment, one guy hand digging to make sure you don't get into any other utilities, and another guy getting the floor busted out in the basement," says Harrington. As long as they don't run into any problems, the whole job should take the team about half a day. Harrington estimates that he could reasonably call in about 20 such teams to work full time until the job is done. Assuming the rate is forty pipes a day, roughly 249 days a year (nights and weekends, y'all), the Flint plumber's militia could bang the job out in just over two years.

Harrington says digging up and replacing a forty foot length of lead pipe costs around $3,000. This does not take into account externalities like repaving streets and sidewalks, fixing any damage done to the home, and resodding lawns. Multiply $3,000 by 20,000 pipes and you get $60 million dollars—which suggests that the figure quoted in Michigan governor Snyder's email is probably a lowball.

Even if the state ponied up to fix the service lines, Flint could face lingering lead contamination from water heaters, faucets, and any pipes inside the person's home laid before 1986—the year lead plumbing was outlawed. "But outlawed doesn't mean removed," says Kaufman. Any brass fixtures could contain some lead, as well as the solders connecting lengths of copper pipe. "It's also the main lines, some of which are over 100 years old and near the end of their life cycle," he says.

Flint is still pushing water through corroded lead pipes, and no authorities have set a timetable for removal. Eventually somebody is going to have to make a decision. Let's hope it's finally a good one.