Impurities in the solution increase the boiling point. This is because impurities decrease the water molecules available for vaporisation during boiling. A greater amount of heat is needed to make the same amount of impure solution to vapourize than the heat that is required to make a pure solution vaporize. Therefore, leading to the rise of the overall boiling point of the solution.
It should be noted that not all impurities raise the boiling point, there are some rare cases in which the impurities decrease the boiling point.. Therefore, it is necessary to know the type of impurities being added to the solution to understand the final effect that the impurities have on the boiling point.