Pollumeter: a Water Quality Index Model for the Assessment of Water Quality

By Hemant Pathak¹ and S. N. Limaye²
January 2011

  1. Department of Chemistry, Indira Gandhi Government Engineering College, Baharia, Sagar, 470004, India
  2. College of Chemistry, Dr. Harisingh Gour University, Sagar, 470003, India
The present work is aimed at assessing the Water Quality Index (WQI) for the ground/municipal/reservoir water of Sagar city. This has been determined by collecting water samples from selected 20 locations covering the entire city, and subjecting the samples to a most important physico-chemical analysis. To create the pollumeter (a model based on WQI), the following 21 parameters have been considered: colour, water temperature, turbidity, TDS, TSS, pH, total hardness, calcium content, magnesium content, total alkalinity, chloride, nitrate, o-phosphate, iron and fluorides present in water samples used in pollumeter. The results of the chemical analysis have been used to suggest models for predicting water quality. The results obtained from the pollumeter reveals that the water quality of the area needs some degree of treatment before consumption, and it also needs to be protected from the contamination. Once the water sources are contaminated, its quality cannot be restored by stopping the pollutants from the source. It therefore becomes imperative to regularly monitor the quality of the water to protect it. The objective of the present work is to create a pollumeter based on computed water quality index values to assess the suitability of water for human consumption.
It thus becomes an important tool for the assessment and management of water body (surface/ground). It is to summarize large amounts of water quality data into simple terms for reporting to management and the public in a consistent manner.

Keywords: Physico-chemical Parameters, Groundwater, Water Quality Standards, Water Quality Index, Regression Analysis


The degradation of water quality in a water body creates adverse condition so that water cannot be used for intended beneficial uses including bathing, recreation and as a source of raw water supply. According to Central Pollution Control Board, 90% of the water supplied in India to the town and cities are polluted, out of which only 1.6% gets treated [1]. Therefore, water quality management is fundamental for the human welfare.

WQI is defined as, a rating reflecting the composite influence of different water quality parameters. It is one of the most effective tools to communicate information on the quality of water to the concerned citizens and policy makers [2].

A pollumeter is an effective tool to assess the quality of water obtained by aggregating several water quality measurements into one number. This simplified expression of a complex set of variables can be used for a variety of purposes, including:

First samples of selected 20 sampling places of Sagar city are tested for desired physico-chemical parameters to determined WQI values. The weightage is given to the parameters according to purpose where most influential/representative parameter for the purpose is given higher weightage than the less important one. The weighted average of the parameter will give the WQI of that sample for the desired purpose. The purpose will also select the choice of the parameters.

The next step will be to select a standard for maximum and minimum permissible limit. Once the results from the sampling is available the weighted average of the values of the parameters are calculated. As mentioned earlier the influential parameter for drinking water is given higher weightage than the other less influential ones [3].

Generally from literature reviews it can be seen that a 100 point water quality index scale can be divided into several ranges corresponding to the general descriptive terms shown in the table below.

Table A · Water Quality Index Legend
Concentration Quality E.I.A.
90 – 100 Excellent Excellent
80 – 90 Good Healthy
50 – 80 Medium Alarming
25 – 50 Bad Badly Affected
0 – 25 Very bad Very Badly Affected

Study area and collection of water samples

Water samples were collected from 20 sampling places (ground/municipal/reservoir water) of Sagar city. Each water sample was taken in PreMonsoon to Post Monsoon during September 2007 to June 2010. The samples were collected in prewashed (with detergent, diluted HNO3 and doubly de-ionized distilled water, respectively) clean polythene bottles without any air bubbles and tightly sealed after collection and labeled in the field.

The temperatures of the samples were measured in the field on the spot at the time of sample collection. The samples were immediately analysed in the chemistry lab to minimize physico-chemical changes. The error due to time has been omitted for the present study. Determinations of the major ions, physical and chemical properties of the water samples were performed on the same day of sampling. Each sample was analysis for, using procedures outline in the standard methods for the examination of water and wastewater APHA [4].

Method and methodology

Analysis of water sample

All the chemicals used were of AR grade. Analysis was carried out for most water quality influencing 21 parameters with concerning units and test methods discussed in table (B).

Table B · List of Physico-chemical parameters and their test methods
Parameters Units Test Methods
1 Water temperature °C Mercury-in-glass thermometer
2 Colour Hz.U. Pt-Co Scale
3 pH - pH meter
4 Turbidity NTU Turbidity tube
5 Dissolved Oxygen (DO) mg/L Winkler method
6 Biochemical Oxygen Demand (BOD) mg/L 5 days incubation at 20° C and titration of initial and final DO.
7 Chemical Oxygen Demand mg/L Open Reflux Method
8 Conductivity ms/cm Conductivity meter
9 Alkalinity mg/L Titration
10 Total Suspended solids(TSS) mg/L Gravimetric (filtration and weighing of residue)
11 Total dissolved Solids mg/L Digital conductivity meter (LT-51)
12 Chloride mg/L Argentometric titration
13 Residual Chlorine mg/L Iodometric
14 Orthophosphate (P043- – P) mg/L Ammonium molybdate ascorbic acid reduction method
15 Nitrate -Nitrogen (NO3 – N) mg/L Spectrophotometric method
16 Ammonia-Nitrogen (NH3 – N) mg/L Spectrophotometric (Phenate method)
17 Total Hardness as CaCO3 mg/L EDTA titration
18 Fluoride mg/L Colorimetric Method
19 Iron mg/L Colorimetric Method
20 Ca Content mg/L EDTA titrimetric method
21 Mg Content mg/L EDTA titrimetric method and calculation

For the desired purpose (say drinking or other uses). WQI may vary with respect to purpose and standards selected. Water quality data used in the pollumeter has been taken from experimental chemical analysis.

For computing WQI three steps are followed. In the first step, each of the parameters has been assigned a weight (wi) according to its relative importance in the overall quality of water for drinking purposes [5]. The maximum weight assigned to that parameter by itself major importance in water quality assessment. Minimum weight assigned to that parameter by itself may not be harmful. Other in the second step, the relative weight (Wi) is computed from the following equation:

Wi = wi⁄∑wi, i = 1 to n

Where, Wi is the relative weight, wi is the weight of each parameter and n is the number of parameters.
Calculated relative weight (Wi) values of each parameter in the third step.
Cumulative relative weight factor (C.W.F.) is the sum of weight factor of all selected physico-chemical factors.

The value of the physico-chemical parameters were compared with desirable/permissible limit of IS: 10500 drinking water specification [6]. The regression analysis [7] has been performed using by Winks SDA 6.0.5, SPSS 11.0 Statistical Software. This is a user-friendly Excel 2007 based model programmed using Visual Basic for Applications. This model has also capable for determine iimpact assessment on aquatic environment of Sagar successfully.

Results and Discussion

Table C · Normal statistics of water quality parameters of ground/municipal/reservoir water samples
Table D · Relative weight of Physico-chemical parameters (mg/l)
Physico-Chemical parameters Indian Standards/ WHO/CPCB, New Delhi (ppm) Weight (wi) Relative weight (Wi)
Total dissolved solids 500-2,000 7 0.07
Alkalinity 200-600 5 0.05
pH 6.5-8.5 7 0.07
Colour 5-25 4 0.04
Conductivity .750-3.0 5 0.05
TH 300-600 5 0.05
Chloride 250-1,000 7 0.07
Residual Chlorine 0.2 5 0.05
Fluoride 1-1.5 5 0.05
Water temperature - 6 0.06
DO 6 or more 8 0.08
BOD 2 or less 5 0.05
COD - 5 0.05
Turbidity* 5-10 5 0.05
o-Phosphate Less than 0.05 3 0.03
Nitrate 45-100 5 0.05
Ca Content 75-200 2 0.02
Mg content 30-100 2 0.02
Iron 0.3-1.0 5 0.05
Ammonia < 0.2 mg/l (up to 0.3 mg/l in anaerobic water) 4 0.04
TSS* 25 5 0.07
∑wi = 100 ∑Wi = 1.00
*Only one parameter is used in TSS or Turbidity at each time
** pH (pH unit), Conductivity (in ms/cm), Colour (Hz.U.), Turbidity (N.T.U.), Water temperature (°C)

A quality rating scale (qi) is consisted of various regression equations. For determination of Q-value, each parameter value is assigned by, after regression analysis of particular parameter (of specific season) with the mean concentration of that parameter of entire study (present in water sample), where mean parameter values taken as dependent variables and seasonal parameter values taken as independent variables, all the regression equations confined within the boundary of its respective standard maxima and minima (in mg/L). According to the guidelines laid down in the Indian drinking water standard for each parameter in mg/L BIS: 10500, 1991/ICMR/CPCB/CGWB.

For computing the WQI, the Sti is first determined for each physico-chemical parameter, which is then used to determine the WQI as per the following equation,

Sti = cwfi.* qi
WQI = ∑ Sti

Sti is the sub index of ith parameter; qi is the rating based on concentration of ith parameter and n is the number of parameters. cwfi. is the cumulative weighting factor.

Table E · Regression equation of various physico-chemical parameters
Dependent Variable Independent Variable Regression Equation
1 Colour mean Colour Colour mean = 6.272292 + 0.5193326 * Colour
2 Temperature mean Temperature Temperature mean = 16.065 + 0.3067092 * Temperature
3 Conductivity mean Conductivity Conductivity mean = 0.2828366 + 0.4501314 * Conductivity
4 Turbidity mean Turbidity Turbidity mean = 6.784838 + 0.3841849 * Turbidity
5 TDS mean TDS TDS mean = 175.5127 + 0.4431936 * TDS
6 TH mean TH Total Hardness mean = 115.7279 + 0.365088 * TH
7 pH mean pH pH mean = 3.746942 + 0.501435 * pH
8 Alkalinity mean Alkalinity Alkalinity mean = 36.22464 + 0.7272103 * Alkalinity
9 Chloride mean Chloride Chloride mean = 10.86802 + 1.095036 * Chloride
10 Residual Chlorine mean Residual Chlorine Residual Chlorine mean = 6.466252E-02 + 0.4908218 * Residual Chlorine
11 Fluoride mean Fluoride Fluoride mean = 1.185041E-02 + 0.7960547 * Fluoride
12 Nitrate mean Nitrate Nitrate mean = 1.075585 + 0.3679061 * Nitrate
13 Ammonia mean Ammonia Ammonia mean = 0.1719322 + 0.1107853 * Ammonia
14 DO mean DO DO mean = 5.01648 + 0.2716102 * Dissolved Oxygen
15 BOD mean BOD BOD mean = 2.486221 + 0.5986784 * BOD
16 COD mean COD COD mean = 7.467968 + 0.2705016 * COD
17 Iron mean Iron Iron mean = 0.254512 + 0.2151515 * Iron
18 Ca content mean Ca content Ca content mean = 49.47815 + 0.1759742 * Ca content
19 Mg content mean Mg content Mg content mean = 9.272231 + 0.1435211 * Mg content
20 O-phosphate mean O-phosphate O-phosphate mean = 1.211008 + 7.967374E-02 * O-phosphate

The pollumeter currently has the following 7 steps:

  1. Parameter
  2. Test result
  3. Units
  4. Q-value
  5. Weighting factor
  6. Cumulative Weighting factor
  7. Subtotal

This water quality index also assessed impact of aquatic pollution on our environment. The standard objectives sheet by default loads all of the variables for which the BIS (IS: 10500-91) /ICMR/CPCB, New Delhi. Drinking water standards has developed water quality guidelines used as a reference.

Working of Pollumeter

An assessment of the water quality of Sagar city (Ground/surface) was studied in September 2007 to June 2010 of Different seasons (PreMonsoon, Monsoon and Post monsoon). Parameters namely - TDS, TSS, Alkalinity, pH, Colour, Conductivity, Total hardness, Chloride, Residual Chlorine, fluoride, water temperature, Turbidity, o-Phosphate, Nitrate, Ca content, Mg content, Iron, Ammonia, Dissolved Oxygen, Biochemical Oxygen Demand and Chemical Oxygen Demand were considered to compute Water Quality Index.

Pollumeter is a 100 point scale that summarizes results from a total of 21 different water quality tests for possible inclusion in an index. Quality determining equations (regression eq.) representing chemical analysis results of 26 sampling places of Sagar city within 25 km circumference. About 21 factors were chosen and some were judged more important than others, so a weighted mean is used to combine the values. So that field measurements could be converted to index values, when test results from fewer than all 21 measurements are available, we preserve the relative weights for each factor and scale the total so that the range remains 0 to 100. The equations used in the pollumeter were developed by the regression methods. After completing the experimental tests, the results recorded and transferred for statistical analysis in SPSS.11 and WINKS SDA software given regression equations. On input a data in regression equations, a numerical value is obtained. For each test, the numerical value or Q-value is multiplied by a “weighting factor.” (See individual tests for more information on Q-value.) For example, dissolved oxygen has a relatively high weighting factor; because it is more significant in determining water quality than the other tests. The 21 resulting values are then added to arrive at an overall water quality index (WQI).

Table F · Pollumeter
Parameter Test Result Units Q-Value Weighting Factor C.W.F. Subtotal
TDS mg/L NM 0.07 NM NM
Alkalinity mg/L NM 0.05 NM NM
pH pH units NM 0.10 NM NM
Colour Hz.U. units NM 0.04 NM NM
Conductivity mS/cm NM 0.05 NM NM
TH mg/L NM 0.05 NM NM
Chloride mg/L NM 0.07 NM NM
Res.Chlorine mg/L NM 0.05 NM NM
Fluoride mg/L NM 0.05 NM NM
Water temp. degrees C NM 0.09 NM NM
DO mg/L NM 0.14 NM NM
BOD mg/L NM 0.07 NM NM
COD mg/L NM 0.08 NM NM
Turbidity* NTU NM 0.05 NM NM
o- Phosphate mg/L P NM 0.03 NM NM
Nitrate mg/L NM 0.09 NM NM
Ca Content mg/L NM 0.03 NM NM
Mg content mg/L NM 0.02 NM NM
Iron mg/L NM 0.05 NM NM
Ammonia mg/L NM 0.04 NM NM
TSS* mg/L NM 0.05 NM NM
*Only one parameter is used in Tss or Turbidity at each time Totals: 0.00 0.00
NM = Not Measured Water Quality Index NM
C.W.F. = Cumulative weighting factor Water Quality Rating NM
Base: Standard Guidelines used from IS:10500 and CPCB, New Delhi
Method: Regression analysis


The aim of the model to be able to input data for a particular water body and, in turn, compute indices for various water uses such as drinking water, aquatic life and recreation simultaneously for comparison purposes. The application of the model is an evolving process and there are plans underway to expand the model in the future to include water uses for aquaculture and agriculture. This particular model allows the user to input site-specific objectives, or to utilize the guidelines for various parameters.

In conclusion, from the results of the present software, it may be said that the pollumeter is absolutely fit for assessment the quality of fresh water. It is recommended that analysis should be carried out from time to time to monitor the rate and kind of contamination. It is need of human to expand awareness among the people to maintain the Cleanness of water at their highest quality and purity levels to achieve a healthy life.


  1. Guidelines for Water Quality Monitoring, Central Pollution Control Board New Delhi, 2007-08, Website: www.cpcb.nic.in
  2. Ramakrishnaiah C. R., Sadashivaiah C. and Ranganna G. E-Journal of Chemistry, 2009, 6(2), 523-530, Website: www.e-journals.net
  3. Venkatasubramani R. , Murali K. , Meenambal T., Nature Env Polln Techno, 2005, 4(2),199-202.
  4. APHA “Standard Methods for the Examination of Water and Wastewater” (American public health association publication, 18th edition, Washington DC), 1992, ISBN 0-87553-131-8, ISSN 8755-3546.
  5. Ramesh S., Sukumaran N., Murugesan A. G., Rajan M. P., Ecological Indicators, July 2010, 10(4), 857-868.
  6. Indian standard drinking water, Specification (First Revision) IS-10500:1991. BIS, New Delhi, India
  7. Rene E. R. and Saidutta, M. B., Int. Journal of Environmental Research., 2008, 2(2), 183-188.


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