Although Water Quality Index (WQI) is usually orientated to qualify urban water supply, it has been widely used by environmental planning decision makers. The quality of the irrigation water has to be evaluated to avoid or, at least, to minimize impacts on agriculture and human health. This paper presents the adaptation of the WQI to WQII in order to identify relevant conditions for the planning of the irrigation water resources. The aggregation of the irrigation water quality parameters, using Electre I/II hierarchic techniques, plus mathematical models from Quality Functions (QF) result in WQII. The obtained results were divided in two groups: WQII1, which includes faecal colimetry, hydrogenionical potential, biochemical demand of oxygen, cloride, total nitrogen, and electric conductivity parameters; and WQII2, which does not consider faecal colimetry in its QF. Piracicaba River watershed (São Paulo State, Brazil) was the study case. WQII1 shows a inappropriated water for vegetables and fruits irrigation, whereas WQII2 defines it as appropriated.
Piracicaba river; water quality; index; irrigation