The article outlines how this shouldn't be possible, which makes me curious as to what happened.

Nothing happened. The tests are broken and people doing the testing aren't intelligent enough to realize it. These are probably urine test kits that aren't even looking for THC, but rather a primary metabolite that is excreted in urine. All kinds of things can trigger a false positive in these tests, especially if you start testing water instead of urine. Water is full of things that you would never expect to find in urine.

Yup, that's the one. That makes a lot of sense.

I don't think stupidity is involved in the testing. They're getting positives for the THC by-products, and those positives weren't coming out in a way that made any sense, so (as you'd hope) the results were kicked up the food chain. The fact that the city is closing down part of its water supply is more a reaction to two factors: 1. unprecedented test data, and 2. having to respond to the inevitable public outcry. They acknowledge that spiking the water with THC is impossible, but they're not the ones that'd go ape if nothing was done. It's better to have the public bitch about not having the "spiked" water than having the nervous nellies running around claiming their kid got high from drinking the tap water.

It was basically a lose-lose situation, as are many when any hot button topic (i.e. drugs) is introduced.

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