200tdi power steering problem

Hi was hoping that someone would have the answer to a problem i have just discovered.I was playing in a flooded car park today in my 90 ,the water was probably 18" deep ,as i was turning the steering wheel the power steering started to go lumpy as if the power part of it was coming and going in stages.I was probably doing 5-10 mph ,when out of the water i sat and turned the wheel back and forth and the lumpyness was there but cleared after a few turns.I have a 2" lift,30mm spacers and its on 265/75/16 a/t tyres .Any one got any ideas ...
Cheers for any help

cos your fan belts are slipping on the pulleys (drives power steering pump aswell as alternator) wiv them being wet

Cheers Stig do you think a new belt is needed or just tightening up if this is poss .. Thanks again