Danger in the Tap

America has a couple of infrastructure problems, namely leaky pipes. They occur everywhere, but not many people pay attention to it until Hell occurs. The Cryptosporidium outbreak in Milwaukee, 1993, killed 69 people, and infecting around 403.000 people.

What would happen if such an outbreak occurred in Washington D.C or New York City? (Likely before 9/11 if you are going with the latter)
 
A Water treatment professional says not really likely.

The Milwaukee Cryptosporidium outbreak in 1993 was like Chernobyl for the water treatment industry. It was a perfect storm of several face palm moments that culminated in the mess you reference.
One, they got hit with a massive dose (100-250X) the normal population of bovine-strain Cryptosporidium most likely due to a feedlot dumping untreated waste into the source water.
(Most cities have an industrial waste surveillance and pretreatment program to at least notice and alert the collections and treatment plant personnel as to what manner of dumps (toxic, grease, flammable, really acidic/basic chemicals) are coming down the pipe.)

Two, the folks testing for pathogens weren't looking for Crypto in their microbial survey, and it took eight days of monkeying around before management shut down the plant.

Three, the operators at the plant didn't backwash their filters properly, figuring the terminal chlorine disinfection would zap whatever left the plant into the distribution system.
As you can tell, Cryptosporidium implies a spore-forming bug that takes a lot more chlorine/radiation/heat to kill than your standard bug.
So let's review-- 100-250X the normal amount of a chlorine-resistant bug coming down the pike of what's normally not an issue nobody knew to brace for, not reducing the turbidity of the water or zapping it with enough chlorine to strain out and kill the microbes present, 400,000 folks got mildly ill and 69 folks died.

Murphy can strike anywhere, so I wouldn't totally rule it out, but the EPA requires distribution systems conveying potable water to have 4.0 mg/l or ppm of chlorine throughout to kill any incidental microbes from leaks
because no system of pipes is 100% leak-proof. Plus, they're supposed to run at 35 psi positive pressure (20 psi minimum when fighting fires) to prevent sucking in trash.
Most water utilities have a write-off level of 5% or so loss due to leaks, because it's expensive in time, money, and man-hours to dig up and replace or patch or resleeve water mains.

You'd need a massive power failure to stop the pumps, and even then, SOP is to send out a boil water notice, shut the system down and hyperdose the system with 50 ppm of chlorine for an hour to zap whatever in the mains if it's been standing any length of time.

Of course, since budget cuts have hit local water utilities and the state regulatory agencies keeping tabs on them for compliance pretty hard, you might have a green crew responding to things and boning up some element of the SOP and still sickening a large # of people.
 
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