Apart from warming up the water, I take it there's nothing inherently pollutant about using it for cooling. Edit: On second read, your point is that heat is a

Apart from warming up the water, I take it there's nothing inherently pollutant about using it for cooling. Edit: On second read, your point is that heat is a pollutant itself. My next sci-fi daydream will be about cooling down the planet by converting atmospheric heat.