I think this paper could be useful for you :

Article EVALUATION OF IRRIGATION WATER QUALITY INDEX (IWQI) FOR AL-D...

WHO standard for drinking water quality is the one which can be referred in general for any region. However for better understanding, applicability and sustainability on regional scale, one has to develop their own WQI based on natural and manmade water quality related parameters/activities/issues.

Dear Mr. Wisam,

The index that you select may vary for the circumstances. So for your circumstance, you are the most knowledgeable to select, one, two or more for your intent and if you want to compare results from your area with results of other areas that use different indices. I can imagine you may have many things to consider. Hopefully, you will find an index or indices that are relatively easy and inexpensive to collect, but are truly reliable and representative of the intent you want to provide.

Article Development of new integrated water quality index (IWQI) mod...

Internationally, you can follow WHO's guideline for drinking water quality from this link: http://apps.who.int/iris/bitstream/10665/254637/1/9789241549950-eng.pdf?ua=1

However, each country has their own legal framework to monitor and control pollution in the water bodies. For example, in Germany:

Federal Water Act (Wasserhaushaltsgesetz - WHG vom 19.8.2002): basic principles for water resource management Federal Drinking Water Ordinance (Trinkwasser-Verordnung - TrinkwV vom 21.5.2001, and revisions, until 2017): Requirements for drinking water quality and based on the regulations of the EC Drinking Water Directive DIN 2000: Guidelines for drawing up requirements for the design, construction, operation and maintenance of public drinking water supply systems If you want to work in Germany as water technologist, you must follow DIN 2000 and LAWA water quality index.

You can follow WHO's international standards & guidelines for the drinking water quality, or your own country national standards.

A number of WQI are detailed in the review below along with their advantages and disadvantages. Kindly have a look

Article Water quality indices- important tools for water quality ass...

Thanks lot my dear

following link may be useful for you.

https://www.gov.nl.ca/mae/files/waterres-quality-background-wqj-39-3-khan.pdf

Please review the following link:

Article Water Quality Index for measuring drinking water quality in ...

Thanks lots dear dr Omar Ali Al-Khashman

You can also have a look at the following paper:

Conference Paper EVALUATION OF DRINKING WATER QUALITY IN TERMS OF WATER QUALI...