There are no international mandatory drinking water standards.The World Health Organization (WHO) publishes Guidelines for Drinking-water Quality which many countries use as the basis to establish their own national standards. The Guidelines represent a scientific assessment of the risks to health from biological and chemical constituents of drinking-water and of the effectiveness of associated control measures. As the WHO Guidelines for Drinking-water Quality are meant to be the scientific point of departure for standards development, including bottled water, actual national standards will sometimes vary from the Guidelines.