Heavy Metal Pollution Index (HPI) is a technique of rating that provides the aggregate
influence of individual heavy metal on the total water quality. The rating is a value
between 0 and 1, reflecting the relative/subjective importance of each quality considerations
and inversely proportional to the recommended standard (Si) for each parameter
(Reza and Singh 2010; Prasad and Mondal 2008; Prasad and Sangita 2008). The calculation
of HPI involves the following steps: