The Regulatory Scan is a report which documents the values specified in national standards for drinking-water parameters and how they compare to those set out in the fourth edition of the WHO Guidelines for Drinking-water Quality. The World Health Organisation’s Guidelines for Drinking Water Quality are an international reference point for the establishment of national regulations and standards for water safety, and along with uptake of Water Safety Planning, the Regulatory Scan represents an important initial step in documenting their influence in the setting of these regulations and standards. The report considers the values specified for chemical, aesthetic, radiological, and microbiological parameters for 100 countries around the world. The report is especially intended for regulators and other key stakeholders in drinking-water quality, who may find it a useful reference point to benchmark their standards against others.