Well I have a couple redundancies...
R/O container:
1: the input water is on a solenoid that is hooked to a timer. The solenoid gets power twice a day for 2 hours that allows the booster pump to turn on and start making water.
2: the float valve in the container is hooked to a pressure switch that turns the unit off when the valve closes and the pressure builds in the line. So if the solenoid fails, the float valve will catch it.
3: I have a float switch at the upper water limit that's wired to the booster pump of the RO. So if the solenoid fails and the float valve fails, the rising water level will hit the switch and then the unit off.
4: I have a output at the top of the container that is routed to the mop sink. So if the solenoid fails, the float valve fails, and the float switch fails the excess water will just empty into the sink.
5: I have a water alarm wired into the piping of the overflow. So if the overflow ever gets wet, the water alarm will text me, and beep really loud.
Heater:
I currently have 4 300w heaters hooked to a surge strip that is hooked to a ranco controller. So 4 heaters have to fail at once for the water to get cold. If one of the heaters gets stuck on. The ranco will detect the rising heat and flip all the heaters off.
ATO:
1: I have a float switch that turns the pump in the RO container on and off.
2: I have a second float switch set a touch higher than the fill switch. So if the fill switch gets stuck on, then the second switch will turn the pump off.
3: the RO water input into the sump comes in via a float valve. There is a "t" on the output of the ATO pump above the highest water level pointing down. So if the water level inside the sump fills to the point that the second switch doesn't work, the mechanical float valve will shut the flow off going to the sump and it will just circulate within the container.
4: the highest acceptable level in the sump is plumbed to a drain in the floor. So if the first switch fails, the second switch fails, and the valve fails, the excess water will just go out the pipe.
5: again, there is a wifi water alarm within the emergency drain. When it gets wet, it screams and blows my phone up.
I have additional wifi water alarms covering the circumference of the sump as well as the display. So if they get wet, my phone gets blown up and an alarm sounds.