I keep telling this to my local water utility but they keep billing me for drawing water from the municipal supply, regardless.

You're paying for the filtration and delivery of it. Feel free to stop paying and go collect and clean your own water.

Dumping superheated water into the reservoir won't have any second order consequences, right?

If the water is superheated, something has gone drastically wrong. The effects of that style open loop cooling do exist, and are well understood already from the power generation industry.