The WW reservoir is a bit of an enigma.
Is the WW fluid light on to show it is empty? This will happen if the reservoir is leaking.
Do you hear the WW fluid pump humming?
The reservoir overflows if too much fluid is put in when refilling.
When the light comes on it takes 4 liter, more than that and it will overflow. You cannot fill it to the filler cap brim.
The WW reservoir often cracks where it is supported.
There is a float inside that switches the low fluid light on, sometimes this jams.
The nozzles can get blocked when slime gets trapped in the nozzle.
There is a thread on how to remove, repair or replace the WW tank. CLICK