LAUSR

Between a third and half of the world’s population depend on groundwater for drinking water supply. However, groundwater of high quality is not ubiquitous and groundwater contamination is becoming a critical issue. Particularly, diffuse pollution by nitrate is a cause of groundwater quality degradation in many countries. Such pollution is especially due to agricultural and livestock practices. Moreover, rural and peri-urban settings are increasingly marked by investments in decentralised water services, mainly on-site sanitation systems and reuse of wastewater. Consequently, problems connecting bacteria and viruses are of increasing concern and can cause health problems of differing severity. From the point of view of governments and other agencies responsible for drinking water supply, methodologies to evaluate a degraded resource and how to regain quality are crucial. In rural and peri-urban settings, there is a need to promote changes in agricultural practices to protect aquifers. This may require farmers to adopt new methods and accept different policies. Their willingness may depend on the awareness of the impact of their practices on water quality. Farmer unions often blame poor on-site sanitation or inadequate wastewater treatment for pollution. Clearly, there is need to discriminate between contamination sources. The main aim of this special issue of Environmental Science and Pollution Research (ESPR) is to focus on diffuse contaminants and related impacts from an interdisciplinary point of view, that spans the technical and social sciences. This issue was made only of invited papers after selection by the guest editors. Year 2016 was a major milestone for the International Association of Hydrogeologists (IAH) and its 43rd Congress, celebrating the 60 years of IAH, was hosted in Montpellier, France, in September. Following the successful session on diffuse groundwater contamination at different scales, especially due to on-site sanitation and agriculture, the Special Issue in ESPR represents an original contribution of the IAH by collecting complementary approaches to this increasingly important subject. Particularly, it analysed field-based studies of diffuse pollution in groundwater and surface water, mainly nitrate and pathogens, and suggested different methodologies (modelling, interviews...) to tackle groundwater resources degradation and to increase awareness also for stakeholders and population. Five papers analysed nitrate pollution in groundwater and surface water. Ouedraogo et al. (2017) assessed the validity of an African-scale groundwater pollution model for nitrate and found it difficult to apply at this scale. Mas Pla and Menció (2018) studied effects of global changes such as climate and groundwater nitrate pollution from a water balance-based analysis of several aquifers at regional scale in Spain. Górski et al. (2017) investigated long-term (1958–2016) water nitrate data from Warta River in Poland, analysing the role of improvement in water and sewage management and a more Responsible editor: Philippe Garrigues