rsenic in drinking water is a global health concern. The WHO guideline of 10 µg/L is considered provisional and WHO recommends that concentrations should be as low as possible. High income, low dose countries have a unique opportunity to lower arsenic concentrations in drinking water. The question, however, is how to achieve this goal. Simply legislating a low criterion may not be an adequate solution. In a case study from Denmark, the effects of lowering the criterion to 5 µg/L was followed over more than a decade. Results showed a wide variety of responses from the more than 100 waterworks that were thrown into non-compliance.