That’s not how modern power plants work. It’s not an open loop to the cooling tower, instead you have a closed loop that gets superheated under high pressure and runs the turbines, but needs to get cooled down before the loop can start over. You cool it down by running the pipes through other water, which evaporated in a cooling tower. The evaporated water takes the heat out of the system, if you returned it to the loop, the system would overheat