A consumption-based approach to trace the effects of income inequality on water pollution responsibility in Egypt: An internal grey water footprint perspective

Ensuring water quality and equality are global goals for sustainable development. This study investigates how Egypt's income and expenditure inequalities affect households' internal grey water footprint (IGWF), i.e., domestic freshwater needed to assimilate pollutants discharged through producing products consumed domestically, allocating water pollution responsibility to final consumers based on their income and expenditure. It calculates households' IGWF of 20 income groups, developing a grey-water extended interregional input-output model combined with household expenditure survey data of 20 income levels. It performs a regression analysis between households' income and their IGWF. The cubic specification best fits the relationship, indicating that high-income levels eventually increase households' IGWF on average. The income elasticity of IGWF (0.81) implies that IGWF grows slower than income on average. However, the rich remain the main IGWF drivers due to their higher overall consumption. The wealthiest 4% are responsible for 12% of households' IGWF, approximately equivalent to that of the poorest 24% combined, dominating 63% of mobility's IGWF and 19% of recreation's. IGWF-Gini coefficient increases as products become more luxurious, e.g., mobility (0.81) and recreation (0.40). This study demonstrates the need to design sustainable consumption policies for income groups dominating specific products' IGWF, reducing Egypt's water pollution while eliminating inequality.