Barring the fact that most pollutants aren't that easy to deal with, I don't think so. I think you'd suffer from a kind of Jevon's Paradox of toxicity, where people would just dump more in, until whatever "ok" threshold previously existed would be breached, and you'd be left in the same situation, just systematically worse.

Right.. Have you considered that a basic order-of-magnitude estimate of scale of water, energy, and pressure requirements make the idea wildly infeasible in practice?

Fair enough, sorry. It's just that your question (and some of your answers) don't seem to be accounting for dealing with the volume change of steam, and how that would be managed.

Also the fact that if you're evaporating the water off anyway, why not just let it escape and concentrate the chemicals, and then deal with them that way? I'd guess most of them would not be in the vapour anyway? (unless they're volatile, in which case they'd probably boil off even earlier)

Re: Lava contact. I don't think the resulting water vapour is much more than 100°C? The phase change takes a lot of energy to phase change, and is still at about 100°C after that, and then the steam would escape very quickly, and be displaced by more water, so it would not have much chance to heat up more. The lava-water interface would always be at about 100°C, give or take a few tens of degrees for the Leidenfrost effect, maybe? I might be wrong here, but I can't see how it would get MUCH hotter than 100°C (assuming normal surface pressure).

Their point, which you quite clearly missed, is that people don't need a steady, reliable, high volume flow of steel delivered to every single home and business.

And maybe you should look into steam engines a little more and check out things like how hot that water actually gets. You're gonna discover that for all the prodigious fuel use, the temperature is far below the goal of 500C and the flow rate far below requirements. But keep up the sass.