1. Water quality indexing – surface water
Gopaul, Pravesh Roy
Nowbuth, Manta Devi
&
Baguant-Moonshiram, Yashwaree

2. AGENDA Water Quality Water quality indexing - methods The study area
Data collected
Analysis
Discussion & Conclusion

3. Introduction
Quality of water – governs the potential use (domestic, agricultural, industrial)
Quantity of water – Q, VR (straight forward answer)
Quality of water – (pH, temperature, turbidity, nitrate level, chloride level, conductivity, phosphate, cadmium, zinc,…..) – several parameters
Interpretation of water quality data are complex

4. Water quality index method
an approach to combine the complex data into a single indicative value.
Several key parameters are aggregated into a single dimensionless number – indicator of quality
A single numeric expression - easily understood by non technical people, for decision making.
Indicative of trends over time
Information for the public (not technical)

5. Water quality index - methods
Concept of WQI – first introduced in Germany in 1848
Mainly qualitative in nature – later on numerical value associated:
Horton’s Index (1965)
National Science Foundation (US) – NSF WQI method (1970)
Modified arithmetic mean (1983), Solway modified weighted sum (1985)
Many countries have adapted their own WQI method: Malaysia,Canada, Poland, New Zealand, India, UK, Taiwan
Minimum Operator - Smith (1990)

6. NSF WQI method (1970)
A physico-chemical water quality index mostly, but also bacteriological to a lesser extent
Four steps:
Indicator selection – (variable of concern – oxygen level, eutrophication, health aspects, dissolved solids)
Indicator transformation – (Dimensionless scale & Rating curve)
Indicator weighting – (Some indicators have a higher importance than others)
Index Aggregation

7. NSF WQI method (1970)
NSF carried out a detailed survey and identified the following key parameters (9), for water quality:
Temperature,
pH,
Dissolved Oxygen,
Turbidity,
Feacal Coliform,
Biochemical Oxygen,
Total Phosphates,
Nitrates &
Total Suspended Solids

8. NSF – Water Quality Index
For each parameter identified by NSF, A rating curve based upon a 100 point scale (A) has been derived.
The Q value (B) is read off from the corresponding curve for a known value of the parameter – here Phosphate level A B

9. NSF – Water Quality index
Water quality factors & weights
Some parameters have more importance than others
A weightage factor is associated with each one.
Parameter
Weights DO
0.17
Feacal C.
0.16 pH
0.11
BOD
Temperature
0.10
Phosphate
Nitrate
Turbidity
0.08
TSS
0.07

10. NSF – Water Quality index
Aggregated value =
Σ Qphosphate*Weightphosphate + QpH*WeightpH + QDO*WeightDO….
Aggregated value compared to NSF WQI legend:
Range
Quality
90-100
Excellent
70-90
Good
50-70
Medium
25-50
Bad
0-25
Very Bad

11. Minimum Operator - WQI
The minimum operator also called the Smith Index (Minimum Operator) - developed by Smith in 1987.
This index gives information for the water quality according to its specific use,
general water quality index,
bathing index,
water supply index and
Fishing - index
It also caters for the problem of ‘eclipsing’ which arises during aggregation process.

12. Minimum Operator - WQI Almost similar steps as for NSF WQI
Different key parameters for different uses (General uses, bathing, water supply, fishing)
Rating curve for each parameter – read off ISUB
For a given water sample, derive the ISUB for all the key parameters
Select the minimum ISUB from this set of value
Parameter DO pH
TSS
Turbidity
Temp
BOD
NH3
ISUB 82 92 86 72 64 84 90

13. MO – Calculating ISUB value
PARAMETERS
STN C1
ISUB VALUE
Dissolved oxygen
6.61 76 PH
7.49
100
Suspended Solids
2.30 96
Turbidity (NTU)
2.40 90
Temperature
25.07 54
BOD (mg/l)
1.77 92
Ammonia (mg/l)
0.29
Log Feacal Coliform (/100ml)
2.86 60

14. Monitoring of water quality
Impact of landuse activities on the quality of water – surface & ground
Samples taken at regular levels (weekly/monthly) – CWA & MoE (Env. Lab.)
Physical, chemical and bacteriological tests – determine pollution level
Typical tests –
pH, temperature, dissolved oxygen, total suspended solids, turbidity, conductivity, nitrate, sulphate, phosphate, chloride, COD, BOD

15. Study area – River Cere Station No. Description Landuse Activities C1
St-Anne Bridge
Residential C2
Near District council
Residential & Commercial C3
Maurice Rousset Bridge
Commercial C4
85km Downstream C3 C5
Cite Hibiscus
Residential & Forested C6
Near Floreal Knitwear
Forested & Sugarcane C7
After Wastewater Treatment Plant
Sugarcane Plantation C8
La Porte Bridge C9
125km Downstream to C8
Sugarcane Plantation & Vegetation
C10
La Porte Village

16. Results -NSF & MO WQI
Results for a specified sample taken at a given point in time.
Note the results at C2 and C9 – different for NSF & MO.
Station Ref.
NSF WQI MO C1
77.71 40 C2
77.29 36 C3
79.43 60 C4
80.57 46 C5
79.00 50 C6
75.14 54 C7
80.43 C8
80.86 72 C9 38
C10
81.00 64

17. Results
The locations of lowest quality is ‘eclipsed’ when the NSF WQI is used, but very obvious using the Minimum operator method.

18. Discussion & Conclusion
WQI – Simplified way of representing water quality information
WQI – used to indicate trends over time and in space
Create public awareness – an effective tool.
River classification – different reach for different uses
MO an improved approach over NSF WQI
Rating curves - to be derived (adapt method locally)
WQI however does not replace/enhance the raw data

19. Thanking you for your attention