Well, he won't get superpowers from a magical sippy-cup for one thing and due to the hilariously strict feudal nature of Bretonnian society, he would have to go on a second quest in order repent for having relations with a peasant before he could continue on his quest to get super powers from correct watery tart.

Despite appearances, Warhammer Fantasy is a Low Fantasy setting.

Magic in general is very rare and magic weapons are next to non-existent; wielded only by the mightiest of heroes and villains.

The Lady of the Lake is the Goddess of the Bretonnian's and is one of the few beings powerful enough in the mortal world that an bestow magical powers onto another being or item.

This is why hundreds of knights go out on quests to try and find her and perform chivalrous deeds in her name in order to prove themselves worthy. But out of those hundreds, only one or two might receive her blessing; but that is no way guaranteed.