Once-through cooling is a heat-rejection design in which a plant draws water from a river, lake, or sea, passes it through heat exchangers to absorb waste heat, and then discharges the warmed water downstream. It is common in thermal power stations and other industrial facilities because it is mechanically simple and can move a large amount of heat efficiently when water is plentiful and cool.
In cyber security, once-through cooling matters because the process depends on accurate sensor data, control logic, and operator visibility. Temperature, flow, and discharge measurements help determine whether a plant can keep running safely or must reduce output. If monitoring is disrupted, altered, or unavailable, operators may miss a rising thermal limit and fail to derate in time. Defenders therefore treat cooling instrumentation, alarms, and fallback procedures as part of industrial resilience, not just plant efficiency. The physical system is simple, but its control data can be a critical operational dependency.