The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about

The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about

a) 0.01 to 0.05 ppm

b) 0.05 to 0.5 ppm

c) 0.5 to 1.0 ppm

d) 1,0 to 5.0 ppm

Environmental Engineering Part 3