How the hell do people use that much water? Are they including water consumption needed for the products we use or? Let's say a flush is 8L and the average person flushes 5 times a day, that's 40L. The average person needs about 2L of water a day. Let's say an average shower is 100L. Cleaning dishes at worst is probably like 20L per person without a dishwasher. That's like 160L of water per day and I feel like most of those were over-estimates. How did they get to that number?

Not only that, but given that heating up volumes of water is basically the metric around which energy units and calculations are all derived, it's easy to determine just how much energy.

Assuming an inlet temperature of a fairly optimistic 60°F or 15.56°C, it takes 12,934,470.48 joules to heat one US gallon of water to 500°C. Or if you prefer, possibly because you're an American used to reading your electricity bill, 3.59 kWh to heat that gallon. Just one.

The EPA estimates that just in the US alone, wastewater plants treat 34 billion, with a B, gallons of water per day. No need to get out your calculator, that's 122,060,000,000 kWh or if you prefer, just under 11.5 times the existing average daily power production of the entire country (10,640,243 MWh, if you're wondering).

So, uh. Yeah. Probably not feasible.

when other cheaper solutions (like not polluting in the first place) exist

That involves convincing your polluting cousin, who doesn't believes climate change doesn't exist, not to buy non-stick pans or not to dump their pills into the toilet.

Edit:

Let's assume that heating water to 500C does what you want it to do.

That's the question I'm asking btw.

fire's always cool in my book.

I think you're doing fire wrong, friendo.

Golly gee, if only there were some form of energy generation that required boiling vast amounts of water to turn into steam. But no, that would be silly.

I thought about this too for a while but I learned that even rain contains microplastics.

That might be possible but there are particles that also will be present in vapor which might be toxic. Simply sending the out into the atmosphere would probably not be a good idea. PFAS for example do not break down under ~400C and just creating a fine PFAS mist is probably not what we want.

But yes, of course while heating up the water there will be residue. How to dispose of that will probably also have to be thought of. Maybe 500C is also the answer, but I don't know.

For simplicity, this process is called clarification.

Unfortunately, coagulants are not effective at removing PFAS. The only effective methods for PFAS removal are adsorption (using granular activated carbon or ion exchange resins) or reverse osmosis filtration. These approaches are not used in traditional wastewater treatment because they are very expensive and are not required to meet registrations. However, potable reuse facilities will use these approaches to further treat wastewater effluent to drinking water standards. This is the future of water supply for arid areas like the southwest USA.

Also PS, the most commonly used coagulants are aluminum sulphate (alum) and ferric sulphate, which are not polymers. Polymers definitely are used (especially where I live) but they are more expensive and thus avoided when not needed.

Same place as nearly everything else, the Sun.

500C is above the critical temperature for water. So it would probably be a supercritical fluid. Unless the pressure was above 10 GPa or so in which case it would be solid.

Its above the critical point, so water will be a supercritical fluid. 370 C already requires 217 atm of pressure.