I'm afraid it won't be very accurate with the very low flow rate you'd get from a tap. Lots of inertia in the mechanical bits.
Anyway, it never turns itself off (you actually have to remove the batteries as there's no power switch) and it does not remember the prior amount if you do turn it off. No idea on battery life as I remove the batteries after each use as I only need the flow rate and not the flow amount, although it's nice to know how much wort has circulated cumulatively after a full mash schedule with a RIMS system.
Anyway, it never turns itself off (you actually have to remove the batteries as there's no power switch) and it does not remember the prior amount if you do turn it off. No idea on battery life as I remove the batteries after each use as I only need the flow rate and not the flow amount, although it's nice to know how much wort has circulated cumulatively after a full mash schedule with a RIMS system.