What else? We are dealing with an ever-changing virus pandemic. FOOTOO-loving white supremacist domestic terrorists. AND?

The chemical involved was Sodium Hydroxide, colloquially Caustic Soda. It is an alkali used to adjust the pH of the water, in very low concentrations.

In high concentrations it will corrode the skin and eyes, but I think (without experimenting) you'd notice an odd taste before drinking much. The reported concentration the hacker set would not be as dangerous, but still enough to be an irritant. I don't think it's absorbed through the skin;  but it makes the skin feel soapy - in fact soap is or used to be, fat dissolved in caustic soda - so you would soon notice it. The problem of course is that the quickest and most effective remedy is washing it away with lots of water. OH...

Washing dishes and clothes with it? Well, detergents and water-softeners are alkalis too. 

Who may have done it and why?

One possibility is somebody with a grudge against the water-company, perhaps a disaffected former employee.

For the News reports I heard commented that the method of attack may have been a type of software developed for remote control of computers, normally and rightly for repair purposes. These don't affect the programmes or operating-system directly, other than switching it to a keyboard and mouse in another location. This is why the operator could see and correct the attack so rapidly, which might have been intended by the hacker but still doesn't explain his motive.

So the investigators would presumably ask if the hacker knew what he was looking at and how the water is treated in that particular plant. It would also make him a coward quite prepared to have interfered with the plant in such a way that it looks as if the culprit was the poor operator. 

It also suggests the water-company may have to overhaul its IT security. I do not know if the affected computer is in the affected water-works, but elsewhere, forming a remote-control system. 

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Back now in the 1980s or even 1970s there was an awful incident in England, when the residents of one town fell ill with a strange illness that turned out be accidental chemical pollution of the water. The chemical involved is a flocculant used to enhance the water-filtering, and normally stays in the filters, stuck to the particles it clears from the water. Investigation discovered the flocculent was delivered by road-tanker, and the driver had inadvertently put it in the wrong tank. An honest  mistake not wilful act but with awful consequences, and the lesson that somehow the equipment and/or operating methods would have be modified to prevent a repeat.