Most people got huge water bills after some time due to COVID-19. I wanted to double-check the calculation because the amount was somewhat big. Unlucky I didn’t find any online calculator that get the job done (there was a one in waterboard, but it has a maximum limit of 60 days). So I went with the default option, Excel. I thought of sharing the excel workbook I used as It might be helpful to others. I really don’t know how the VAT calculation is done, so I used 8%. (Thanks to Madura for the suggested edit)
These are the supporting document I used.