Water reuse in Portugal: New legislation trends to support the definition of water quality standards based on risk characterization

Abstract

The increasing demand for water for multiple purposes and the intensification of severe weather conditions due to climate change have put significant strain on freshwater supplies. Portugal can be very vulnerable to climate change impacts and the use of reclaimed waters has been identified as a suitable alternative water source to overcome water shortages. To face the absence of legislation, Portugal has recently approved a policy for the production of reclaimed water from several sources to use in multiple non-potable purposes. The legislation is supported on the recent developments at European Level and its main basis are the international guidelines developed by the International Organization for Standardization, namely for irrigation, urban uses and health risk assessment. Since water reuse can pose risks to health primarily due to pathogenic microorganisms, the new policy defines that all reuse projects shall follow a risk assessment. Besides quantitative assessment should be desirable, these models are complex and presents a high uncertainty insofar requires extensive local data that are not often available for non-potable uses. In this work is presented the brief history of the water reuse in Portugal and a conceptual methodology developed to deal with the limitations on risk assessment. The method involves a strategic appraisal sustained on a semi-quantitative approach for risk characterization to validate the quality standards that meets the needs of the project. The methodology comprises the use of an empirical qualitative judgment to assess the relative importance for hazards, exposure routes and scenarios of contact and multi-barriers in place.