How do you manage on-call duty?
Do the plants have a remote management/monitoring system that tracks issues arising outside regular working hours? A simple solution is to program a reporting function that alerts a mobile phone via SMS, for example. Then, depending on the equipment in place, a morning visit to check the previous day's reports and ensure nothing abnormal has occurred. That way you can anticipate potential system failures. This is how we do it for the wastewater treatment plant. For lift stations, we only have to respond to "critical" alarms on the network (2 pumps disconnected, power failure, etc.).
I am surprised that there isn't a protocol already in place.