TC reported there was no water releasedfrom wiper. TC also feedback hissing sound was heard from th e 'A' side wiper and the sound gone at MSL NB. MR Pressure: 9 bars. ~~~~~ 3668 TC reported there was no water released from wiper. TC also feedback hissing sound was heard from the 'A' side wiper and the sound stopped at MSL NB. MR Pressure was stable at 9 bars, and TC subsequently feedback that MR pressure charged up to 10 bar. Train was reformed to scheduled withdrawal to UPD. CE checked & found 3668 No air leaking.    Suspect water tank empty. MR 9 to 10 bars - ok.  3668 wiper tank found empty. Retopped wiper tank & function check wiper - OK.  Lee PT 44603