Table 2.

Improvement in water quality observed across the world during COVID-19 lock down

Sl. No	Name of the country and study details	Water pollution parameters	Reductions/ Improvements achieved	Reference
1	India, Ganges river	Dissolved oxygen Biological oxygen demand (BOD)	23% 25%	Lokhandwala and Gautam 2020
2	Nepal (Bagmati river basin)	Dissolved Oxygen BOD COD	DO increased by1.5 times BOD decreased by 1.5 times COD decreased by 1.9 times	Pant et al. 2021
3	Turkey (Meriç-Ergene river Basin, especially Ergene river and Çorlu stream)	Metals (Cr, Ni, Zn, Cu, As, Pb and Cd) Total hazard index values for children and adults Total carcinogenic risk values for As Total carcinogenic risk values for Cr	Metal concentrations decreased significantly Total hazard index values for children and adults reduced by 67 and 69% respectively for As reduced by 60% for Cr reduced by 94%	Tokatali and Varol 2021
4	Malaysia (Putrajaya lake)	BOD COD TSS Water Quality Index (WQI)	Considerable decrease in BOD, COD TSS WQI improved from class 2 to 1	Najah et al., (2021)
5	China (Min river)	TSS	TSS decreased by 48%	Xu et al., (2021)
6	India, Subsurface water, Coastal city, Tuticorin (March’2020 to May’2020)	Arsenic Cadmium Selenium Iron Lead Nitrate Total and faecal coliform	51% 50% 42% 60% 50% 56% 52 & 48%	Selvam et al, (2020)
7	Morocco, Boukhalef river (April 2020 measurements compared with April, 2019)	Escherichia coli	Decreased	Cherif et al, (2020)
8	South Asian countries (Pakistan and India)	coastal water quality, phytoplankton densities and algal blooms investigated using changes in chlorophyll (Chl-a) and turbidity	50% reduction in Coastal Chl-a and 29% reduction in turbidity was observed	Shafeeque et al., (2021)