“…However, this effect could be negative, at least for some range of w, if other roles of water were considered, namely its complementarity with polluting inputs in the production of y (for instance, in agriculture, water allows plants to absorb nitrogen and phosphorus more efficiently decreasing the presence of these elements in topsoil) and its own dilution effect (if all the contaminant load is already being carried down, the addition of extra water will improve the quality of the leachates that reach the aquifer). Examples of pollution production functions for nitrates in agriculture can be found in Vickner et al [21], Larson et al [9], and Helfand and House [8]. Following the contamination literature (see Yadav [24] for nitrates, Anderson et al [1] for pesticides), it is assumed that there is a constant natural decay rate for the pollutant, so that contamination would evolve according to:…”