Water quality of Balili River before, during and after COVID: lessons learned and ways forwards for tropical river remediation

Improvement in water quality of several rivers was noted during COVID lockdowns by several studies but no report was dedicated to trace the water quality after COVID. Our study observed the water quality of Balili River, Philippines from 2018–2023 to address this data gap and learn lessons and ways forward towards the attainment of SDG 6 Water and Sanitation. The river exhibited significant improvement during COVID at TSS, color, DO, BOD, PO4 and Cl. The cumulative parameters namely water quality index and comprehensive pollution index showed that the water quality of Balili River improved during COVID at 27–40% but deteriorated again after COVID, though not as polluted as the pre-COVID state. The fecal coliform got worse during COVID but drastically improved after COVID. The water quality generally is worst during dry season then improves in the rainy months due to dilution from rain. These results show that upland tropical rivers, particularly in the case of Balili River, Benguet, Northern Philippines has a natural means of purification namely dilution from rain. Hence, the floating constructed wetland could be implemented during dry months starting from November to May. During heavy rains, the floating constructed wetland could be allowed to be swept downstream, allowing dilution as the next mode of remediation. Then after the rainy season, another floating constructed wetland would be established for another cycle.