I believe it’s still the case that almost all production vehicles use a belt to run the water pump and A/C unit off the motor. I remember driving an under-powered 4-cylinder car once that told you the instantaneous gas mileage, and when I turned on the A/C the mileage dropped 3 mpg from the extra work the engine had to do to drive the compressor, but why do they still use this system?
The alternator is generating plenty of electricity to drive all kinds of devices. There must be a very good reason not to have an electric water pump or A/C compressor instead of one driven by a belt, which can sometimes fail catastrophically.
If you’re a car company striving to increase gas mileage why not make the switch?