My understanding is that with most current reactors there is an inner loop that is constantly recirculating (reactor to turbine) that does not leave containment

My understanding is that with most current reactors there is an inner loop that is constantly recirculating (reactor to turbine) that does not leave containment. This goes through a heat exchange with other water to jettison waste heat from the system. This waste heat can be something like taking water from a river and ejecting it back into the river, just slightly warmer. I’m curious how much using less water actually matters. It’s not like the jettisoned water is dangerous or radioactive