... Carries just enough water to sound plausible.

It's not even close to plausible. It gets legs because it is appealing to think "they" are just that evil and that all our problems can be easily solved once "they" are out of power.

I think there are other conspiracies within the automotive industry that are true, i.e. could have done better for fuel economy but would have impacted profits. The water car is not one of them. There are applications that use water to change engine dynamics that are viable (my dad had a patent on one and lived his life battling people who didn't want to hear about it), but running on water is too far from reality.

If you're in a dry, hot environment and evaporate water in a swamp cooler, you lose about 2.3MJ/l (0.6kWh/l), from which you can skim maybe ~10% (0.06kWh/l) with a thermocouple. If you're charging a Dacia Spring consuming 156Wh/km, you'd have to evaporate ~300 liters of water to drive 100km. (Edit: some errors.)

https://en.wikipedia.org/wiki/Enthalpy_of_vaporization#Other_common_substances
https://en.wikipedia.org/wiki/Thermoelectric_generator#Efficiency
https://ev-database.org/cheatsheet/energy-consumption-electric-car

But then, what if you bought solar panels and a wind turbine instead of thermocouples and water?

Didn't have to be real, just scary to the powerful.

(Not commenting on truth of whether it happened or not, just a generalization of my observations of the behaviours of the powerful)

He believed that the Earth had “fluid electrical charges” running beneath its surface, that when interrupted by a series of electrical discharges at repeated set intervals, would generate a limitless power supply by generating immense low-frequency electrical waves.

https://thefifthestate.com.au/energy-lead/energy/nikola-tesla-dreamed-of-free-electricity-what-happened/

In recent experiments I have discovered two novel facts of importance in this connection. One of these facts is that an electric current is generated in a wire extending from the ground to a great height by the axial and probably also by the translatory, movement of the earth. No appreciable current, however, will flow continuously in the wire unless the electricity is allowed to leak out into the air. Its escape is greatly facilitated by providing at the elevated end of the wire a conducting terminal of great surface, with many sharp edges or points. We are thus enabled to get a continuous supply of electrical energy by merely supporting a wire at a great height, but, unfortunately, the amount of electricity which can be so obtained is small.

https://teslauniverse.com/nikola-tesla/articles/nikola-teslas-free-energy-documents

I read a variation of this years ago though the author of the one I read may have embellished it somewhat.

‘Yes, Nikola Tesla demonstrated wireless power transmission, but not quite in the way people often imagine.

In 1899, during his experiments in Colorado Springs, Tesla managed to wirelessly light incandescent lamps over a short distance (about 25 miles is sometimes claimed) using resonant inductive coupling. He used a large Tesla coil to create high-voltage electrical fields, which could transfer energy through the air. Some reports suggest that he successfully powered a bank of light bulbs several miles away, though there is no definitive proof.

Tesla’s ultimate vision was Wardenclyffe Tower, a massive structure designed to transmit electricity wirelessly across vast distances. However, the project was never completed due to financial issues and skepticism from investors like J.P. Morgan.

So while Tesla did achieve wireless power transfer over short distances, the idea of lighting bulbs miles away in a practical, controlled manner remains largely theoretical.’