Water reuse is a widespread practice in most Mediterranean countries. Some countries have no wastewater treatment facilities and direct reuse of raw wastewater is occurring while others have a well-established national reuse policy. Water reuse microbiological standards, when existing, significantly differ from one country to another. Some countries have adopted regulations close to the California's Water Recycling Criteria whereas other countries have chosen criteria based on the World Health Organisation (WHO) guidelines. California standards are technologically based requirements aimed at eliminating the presence of pathogens. The WHO guidelines relied on epidemiological evidences though few were available. Their revision on the basis of new epidemiological investigations and quantitative microbiological risk assessment (QMRA) provided by Blumenthal et al., together with added QMRA data, helped proposing Mediterranean guidelines. Acceptable annual risks related to bathing and potable water drinking were taken as benchmarks. This proposal is designed to protect individuals against realistic maximum exposures and to provide minimum and affordable requirements which should constitute the basis of water reuse regulations in every country of the region. Inadequacies of the actual knowledge do not allow a definitive position regarding the guideline limits; other scientific and technical basis are still required.

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