A water quality index provides a single number (like a grade) that expresses overall water quality at a certain location and time based on several water quality parameters. The objective of an index is to turn complex water quality data into information that is understandable and useable by the public.

WQI aims at giving a single value to the water quality of a source by translating the list of parameters and their concentrations present in a sample into a single value, which in turn provides an extensive interpretation of the quality of water and its suitability for various purposes like drinking, irrigation, fishing etc.

to know how to calculate the WQI and the equation variables please read these two paper:

http://link.springer.com/article/10.1007/s13201-016-0451-y

http://pubs.sciepub.com/ajwr/1/3/3/

also you can use this site to calculate your WQI directly by putting your parameters:

http://www.water-research.net/index.php/water-treatment/water-monitoring/monitoring-the-quality-of-surfacewaters

so it is type ofequation that you can put your variables and get the final number that can express the quality of your water.

Kind Regards,

you can search for water quality index or NSF water quality index in google and/or researchgate

Water quality index is a 100-point scale that summarizes results from a total of nine different measurements when complete: reported in  the book Field Manual for Water Quality Monitoring, of the National Sanitation Foundation

A water quality index provides a single number (like a grade) that expresses overall water quality at a certain location and time based on several water quality parameters. The objective of an index is to turn complex water quality data into information that is understandable and useable by the public. This type of index is similar to the index developed for air quality that shows if it’s a red or blue air quality day. The use of an index to "grade" water quality is a controversial issue among water quality scientists. A single number cannot tell the whole story of water quality; there are many other water quality parameters that are not included in the index. The index presented here is not specifically aimed at human health or aquatic life regulations. However, a water index based on some very important parameters can provide a simple indicator of water quality. It gives the public a general idea the possible problems with the water in the region.

There are several types of water quality indices but one used by many communities for characterizing overall water quality. This index was originally developed by the National Sanitiation Foundation (NSF) (Brown and others, 1970)

142 water quality scientists were surveyed about 35 water quality tests and asked to consider which tests should be included in an index (Brown and others, 1970; Mitchell and Stapp, 2000). Nine water quality parameters were selected to include in the index. These parameters are:

dissolved oxygen (DO)

fecal coliform

pH

biochemical oxygen demand (BOD) (5-day)

temperature change (from 1 mile upstream)

total phosphate

nitrate

turbidity

total solids

http://www.water-research.net/index.php/water-treatment/water-monitoring/monitoring-the-quality-of-surfacewaters

http://bcn.boulder.co.us/basin/watershed/wqi_info.html

http://bcn.boulder.co.us/basin/watershed/wqi_nsf.html

Article Application of water quality index method in water quality assessment

Article Water Quality Assessment in Terms of Water Quality Index

Check: www.incedi.org/2016

Take care wit its use. Some includes in the index elements or substances thatr are nutrients what  gives low results in samples  which are contaminated.

The WQI is a unitless number ranging from 1 to 100; a higher number is indicative of better water quality. Scores are determined for temperature, pH, fecal coliform bacteria, dissolved oxygen, total suspended sediment, turbidity, total phosphorus, and total nitrogen..

Care!

there are published indexces that incvudes other parameters not strictly contaminants.

You may also like to see this approach. hope you find this interesting

Article Comparative evaluation of water quality zonation within Dwar...

What are the formulars for some specific wqi parameters

Dear Heba,

Water quality index is a set if formulas which helps us to get single numerical value to define the quality of water based on water quality paramerers. For that purpose there are so many well developed indices, but the newly developed Integrated Water Quality Index is very easy to calculate, unbiased and considers n number of parameters. I will suggest you to go through this publication, which will help you to understand.

https://www.researchgate.net/publication/331009233_Development_of_new_integrated_water_quality_index_IWQI_model_to_evaluate_the_drinking_suitability_of_water

https://www.researchgate.net/publication/331009233_Development_of_new_integrated_water_quality_index_IWQI_model_to_evaluate_the_drinking_suitability_of_water

Water Quality Index Calculator - Water Research Center

https://www.water-research.net › watrqualindex

Calculating NSF Water Quality Index (WQI).

WQI is calculated by an equation which considers the ratings and weight of the parameters studied. It could be obtained from many literature.

Hello Dr Heba Hathout

Calculation method of Water quality index (WQI)

See also attached file for formulas

In the first step the selected water quality parameters (TDS, pH, Ca2+, Mg2+, Na+, HCO3-, K+, Cl-, SO42-, NO3- were assigned a weight according to its relative importance in the overall quality of groundwater for drinking purposes. The maximum weight of 5 is given to: TDS and NO3- because these parameters are important indicators for assessment of the overall water quality.

Water quality index was calculated according to the following equation:

📷

📷(1)

(2)

Where: “Wi” is the relative weight; “wi” is the weight of each individual, “Ci” is the observed concentration of each chemical element in each groundwater sample, and “Si” is the corresponding standard values for each chemical parameter (Bouderbala and Gharbi 2017). Table 4 shows the relative weights of chemical parameters.

The classification of water quality is essential for an assessment of the suitability of water for domestic purposes. The water quality is excellent when WQI < 50; water quality is good when 50 ≤WQI < 100; water quality is poor when 100 ≤WQI < 200; water quality is very poor when 200 ≤WQI < 300; if WQI ³300, groundwater is unsuitable for drinking purposes (Bouderbala and Gharbi 2017).

References

Bouderbala, A., & Gharbi, BY. (2017). Hydrogeochemical characterization and groundwater quality assessment in the intensive agricultural zone of the Upper Cheliff plain, Algeria. Environmental Earth Sciences, 76. doi:10.1007/s12665-017-7067-x.

Best Regards

Fatah BOUTELDJAOUI

Dear Heba Hathout ,

you can also have a look at the following file for the calculation procedures.

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

It is an equation with different types of parameters, some of them mandatory and others elective, depending on the method pursued.

Article A recreational water quality index using chemical, physical ...