His point is if it were truly lethal they wouldn't just add it to the public water supply like that, or hastily dispose of what might be a biohazard in a public trash can.

In other words the TSA is full of shit.

I mean, if someone wanted to put poison in the (waste) water supply, they could just pour it down their own drain. It's not like the TSA has special drains. I think it's fair for them not to worry about poisoning the water supply any more than anyone else does.

I don't think anybody is worried about the water being unsafe except for the TSA, who are hastily discarding it. So no, if they are taking the stance that the water might be unsafe, they are responsible for disposing of it safely.

There are things you don't pour down the drain because they can react with your piping, sewage lines and equipment in downstream treatment facilities. There are regulations and protocols for getting rid of such waste, and pouring them down the drain isn't one of them.

The point is that they're mixing the suspect chemicals, no?

And if they have to assume it isn't water then why not handle it as such? As it stands now they have bins for travelers to discard their potential explosives (water bottles) in.