Whenever an alarm sounds at a power plant, sirens go off and warning lights appear in the control room.  A pump failure, pressure loss, and a small water leak may not be a major cause of worry, but multiple alarms will result.  The cacophony of light and sound can be overwhelming to the plant operators, and "Acknowledge" is the button they push to indicate that they know there's a problem and they don't want to hear the sirens and alarm bells.  Which just goes to show that power is a relative thing.