The national water quality index showed 44% of urban monitoring sites recording poor or very poor quality in 2011 (Figure 1.16). This means water quality after conventional treatment is insufficient for public supply, requiring advanced treatment. The main problem affecting surface water quality is wastewater discharge, both treated effluent and domestic wastewater. The deterioration of water quality is usually related to increasing wastewater volumes, reflecting population growth and urbanisation, which were not matched by investment in wastewater collection and treatment systems (ANA, 2013, MMA, 2015a, also see Chapter 3).