Straight from the FCOM :
ROW is armed below 500 ft until the aircraft touches down, independently of the braking means chosen by the flight crew (i.e. autobrake, or pedal braking), when ROW detects the landing runway.
L2 In basic autobrake mode or pedal braking, ROW detects the landing runway between 500 ft and 300 ft RA.
If the flight crew selects BTV autobrake mode, the BTV function detects the landing runway at 300 ft. The BTV function performs a late detection of the landing runway in order to favor the landing runway selected by the flight crew as long as possible.
L1 ROW detects a possible runway overrun when the aircraft is in flight, considering different parameters such as the aircraft weight, the aircraft speed, the aircraft altitude, the aircraft position, the wind.
If ROW detects a possible runway overrun, ROW activates aural and visual alerts to inform the flight crew of the situation.
ON WET RUNWAY
ROW computes two lines: I.e. one WET line and one DRY line. These lines correspond to the minimum landing distance for a WET runway and for a DRY runway.
The flight crew uses the appropriate line as reference depending on the actual runway condition, i.e. dry or wet.
ROW informs the flight crew via a visual alert on the PFD IF WET : RWY TOO SHORT , meaning that if the runway is WET, the landing distance computed by ROW is too long.
CAUTION:
If the runway is WET, and "IF WET: RWY TOO SHORT" is displayed on the PFD, the flight crew must perform a go-around.
In the case of a dry runway, the flight crew can continue the landing.
PFD: IF WET RWY TOO SHORT