How would you confirm that colourless liquid given to you is pure water?

Every liquid has a characteristic boiling point at 1 atmospheric pressure. Boiling point of pure water is 373K at 1 atomspheric pressure. If the given sample is colourless liquid and boils at exactly 373K at 1 atmospheric pressure, then it is pure water. If the boiling point is even slightly above 373K, then it is contaminated.