You need to flush the washer bottle out - hot (like boiled kettle) water and white vinigar always works for me, go for a litre of each. Whack it in there and empty it onto the windscreen using the washers. Change the wiper blades, again and use some ready diluted screenwash - Halfords premium is pretty good, IMHO.
Also well worth a punt is a full-on RainX treatment. Give the glass a bloody good clean and then apply the RainX as prescribed on the bottle. Ruddy marvelous stuff, anything over 40 and the rain eff's right off the glass with no wipers required. When you do use them they whip over the glass and it seems to stop the grot from sticking quite so bad. Well worth 6 quid, dont bother withthe antimist or glass cleaner though. Antimist is crap and glass cleaner no better than Mr Muscle, their screenwash is crap too