Depends on the initial use. Water treatment is a surprisingly interesting (to me at least) rabbit hole.

You don't really control the upstream: someone flushing their toilet, or a laundromat dumping solvents down the drain?

But it's a solved problem to continually test the incoming water supply for the basics (pH, TDS). Plus intermittent checks for full workup (heavy metals, etc).

After that, it's a question of working it through the appropriate steps to get it to the state you want. Sort of like a continuously operating manufacturing line, except you get to blend the product at the end and only have to QA the blended result.

As someone quipped, "Dilution is the solution." Given enough volume and time, you can dilute even an arbitrarily large amount of lead to safe levels.

I've got news for you: wild animals shit on your food crops all the time.

My father was in livestock pathology and always had a chuckle whenever spinach or (insert product here) would claim field contamination.

His verdict: 9/10 it's rat feces at the processing or packaging plant.

But from a marketing perspective, field crop contamination is an act of God. Can't be helped.

Plant contamination would actually mean someone was at fault. And would require (expensive) changes.

The issue when it's people is it let's parasites enter a lifecycle which isn't complicated. Human feces is more likely to have parasites infectious to humans

Right but apparently that doesn't kill me. The question is what happens to industrial runoff in the water stream and if that has any effect on food safety.

I think (someone correct me if I'm wrong) US stormwater / runoff systems have to be isolated from sewer systems. Maybe an EPA requirement?

So reclaimed water is typically dealing with "anything anyone puts down a piped drain in their house."

(That said, I think there are also runoff processing requirements before discharge into waterways too)