When the heat removal demand ...

When the heat removal demand is sufficiently large (100 MW and above), some cities may have treated effluent available from the POTW, even piped into the locale of the plant.  Sometimes this water  may already have been spoken for to the extent allowed by the city permit (requiring them to continue to release X amount of water per day to streams, or rivers.  Alternative sourcing really depends on site location, availability of water from the start, permitting, and a sundry of other legal and environmental issues which could come into play.