Water Quality Indices (WQI) - Water Quality Management: Assessment and Interpretation - page 20

Chapter 3
Water Quality Indices (WQI)

Abstract Having a lot of data for different water quality parameters in surface
water without proper interpretation are not useful for water quality management.
Due to the extent of water quality parameters, water quality indices (WQI) could be
used as a point scale for interpretation of these parameters. WQI is the essential
prerequisite of water quality management. Since 1978, much effort have been done
to present techniques to summarize water quality data to a de ned numeric digit

which describes the degree of water quality. In this chapter, at the

rst step, the
historical background of WQI was reviewed. Afterward, National Sanitation
Foundation s Water Quality Index (NSFWQI) method and British Colombia water

quality index (BCWQI) Method that are used frequently, described in details.
Finally, the application of NSFWQI in the K

'

d River, which
located on the south-west and north of Iran, were described. In addition the WQI of
the Sef

ā r ū in River and Sef ī d-R ū

ī d-R ū d River was investigated by BCWQI.

3.1 Historical Background

Huge amount of water quality data without precise interpretation cannot help water
quality management properly. Therefore, it is necessary to summarize water quality
data to a de ned numeric digit which indicates the degree of water quality. To solve

this problem there is a technique which is called water quality indices. Water
quality indices are methods that can help water quality management to determine
existing water quality.
A survey on the types and extent to which water quality indices are being used in
the USA was conducted by Ott ( 1978 ). It is; however, noteworthy that comparison
of different indices is rather controversial since the underlying assumptions and the
aim of the different applications vary (Canter 1985 ).
Schaefer and Janardan ( 1979 ) studied five water quality indices among which,
two indices, P1 and I, employed to rank data and followed the beta distribution.
These two indices, which are true statistical measures of water quality, can be used
with any set of water quality parameters, and also correlate highly with biological