Simulating the impact of water pricing on household's behaviour: the temptation of using untreated water

Recent studies on urban water demand have suggested that the water price increase observed during the last ten years in France has led to a reduction in the consumption of urban water by households. Whereas certain households have reduced their water consumption, others have turned to substitute water resources (collection of rainwater, borehole drilling, wells supplied with untreated mains water, grey water recycling systems, etc.). This article presents the results of a case study, which describes and analyses the phenomenon of resorting to untreated groundwater as a complement to or a substitute for the urban water supply. After highlighting the risks associated with uncontrolled development of private boreholes, the paper presents a survey conducted in Southern France to understand the motivations of households drilling boreholes. The results of this survey are utilised to develop a micro-economic model of households' behaviour, which is then used to assess the probability of development of private boreholes on a regional scale. The impact of various economic and regulatory scenarios on borehole development and the related impact on urban water demand and financial sustainability of water and wastewater management utilities are assessed.