Water Quality Indices (WQI) - Water Quality Management: Assessment and Interpretation - page 25

3.2 Summary of WQI Methods

WQI can generally be divided into five groups, which are as follows:

￿ General WQI methods:

These can be applied to determine the overall water quality. They do not;
however, take into account the water usage.

￿ Speci c WQI techniques:

These are employed to de c usage such as drinking,

irrigation, industrial and protection of the aquatic life.

ne water quality for speci

Design Index:
They enjoy immense use in decision making processes in management. In such
cases, water quality classi

￿

cation is not taken into account. These methods are
merely tools to help assess the impact of decisions and plan future measure for
water management.

Statistical Index:
Statistical indices are perhaps the most objective methods in service for water
quality classi

￿

cation. Since they use statistical models, little individual judgment

is present.

Biological Index:
These classi

￿

cations de ne water quality according to the effects of water on the

aquatic life.

In each of the above mentioned general categories, researchers have developed
many methods to assess water quality that employ diverse water quality parameters
and mathematical equations.
Two methods of water quality indices described in detail which are as follows.

3.3 National Sanitation Foundation s Water Quality Index

'

(NSFWQI) Method

With the support of the National Sanitation, Brown et al. ( 1970 ) presented an index
for water quality. Their work can be summarized as follows:
First, Brown et al. ( 2000 ) prepared a questionnaire (No. 1) and sent it to a carefully
chosen panel, whose members came from a variety of backgrounds including reg-
ulatory of ces, local utilities management, consulting engineers, academics and

waste control engineers. They were asked to consider 35 water quality parameters for
possible selection in a water quality index. The panel members were also asked to
give an importance rating for each parameter on a scale of 1

5, where 1 corresponded

-

to the highest signi cance while 5 corresponded to the lowest signi cance.

cance of each
parameter for the index, a second questionnaire was prepared in which each
member was asked to review the original rating while considering their peers

To obtain greater convergence of opinion regarding the signi

'