When would low-flow not be suitable?

Low-flow would not be suitable when the well is extremely low-yield. If you can’t get the water level to stabilize at some reasonable pumping rate, at least 100 mL/min, then do not use the low-flow approach, switch over to passive or no-purge sampling. Other than that, low-flow would not be suitable if the time required for low-flow purging and sampling was just too long, and/or the process was too arduous.