The water molecule is polar and this property if given by the geometry of molecule and the difference of electronegativity.
Since the ruler material is not specified, one can suppose that it is a plastic ruler since only plastic material can become charged by rubbing process. Since plastic has no electrical conductivity, the negative charge will remain in the rubbed region.
You need to remember that the opposite charges attract each other, hence, when you rub the ruler with the piece of fur, the ruler will become negatively charged, while water will have a partial positive charge on hydrogens.
Because the ruler and water have the opposite charges, they attract each other.