WATER QUALITY ASSESSMENT AND REPORTING 1

3.7. WATER QUALITY ASSESSMENT AND REPORTING Diederik Rousseau UNESCO-IHE Institute for Water Education Online Module Water Quality Assessment 2

CONTENTS 1.Definitions 2.Composition of Water Quality Indices 3.PRATI index 4. Reporting 3

“The evaluation of the physical, chemical and biological nature of water in relation to natural quality, human effects and intended uses.” Water quality assessment makes use of the data collected during the water quality monitoring. Water quality assessment results in the last, important stage of the whole process, i.e. reporting. Definition of water quality assessment 4

1.Decide on which data to use (all data, monthly averages, 90 th percentile,..) 2.Compare data with WQ standards, or 3.Lump data together into a single value which is called a WATER QUALITY INDEX. How to assess water quality? 5

A WQ Index is defined as: A simple expression of a more or less complex combination of a number of water quality parameters which serves as a measure for water quality. The index is presented as a number, a class, a verbal description, a unique symbol or a color. Advantage: reduced complexity (many data compressed into one single value) Disadvantage: loss of information Water quality indices 6

EXAMPLE: Water quality data of the UK Environment Agency. Data on dissolved oxygen, biochemical oxygen demand and ammonia are joined into a single GQA indicator which is represented by different colors. 7

CONTENTS 1.Definitions 2.Composition of Water Quality Indices 3.PRATI index 4. Reporting 8

1.selection of the parameters; 2.determination of the quality scores per parameter: the sub-indices; 3.determination of the WQ Index by aggregation of the sub-indices. Three steps to compose a WQ Index 9

At least 2 parameters are needed Choice depend on objectives, Examples: If you are interested in eutrophication you could make an index based on N and P data If you are interested in the effect of wastewater, you could make an index based on BOD, NH 4 (important components of wastewater) and DO (remember the oxygen sag curve) Step 1 – selection of parameters 10

For each one of the selected parameters, the value needs to be translated into a score Hypothetical example for DO: < 5 mg/L  score 0 ≥ 5 mg/L  score 1 OR Score = (DO concentration / 10) e.g. DO = 5 mg/L  score 0.5 Step 2 – subindices 11

Step 3 – aggregation of subindices Based on product rather than sum 12

CONTENTS 1.Definitions 2.Composition of Water Quality Indices 3.PRATI index 4.Reporting 13

Subindices in the PRATI index Kubel test = a test for small amounts of organics in water, which involves boiling the water with potassium permanganate for 10 minutes. ABS = alkyl benzene sulfonate (used in detergents) CCE = calcium carbonate equivalent, a measure for alkalinity Read: ; ; 0.37; ;

PRATI indices Arithmetic means of the following subindices: Basic PRATI index = BOD, DO and NH 4 Simplified PRATI index = pH, DO, BOD, COD, SS, NH 4, NO 3 and Cl Full PRATI index = all 13 subindices 15

Exercise (the answers will be discussed during Course 3) Calculate the basic, simplified and full PRATI index for the following dataset: ParameterValueParameterValue pH7.9NH mg/L DO67%NO 3 52 mg/L BOD 5 23 mg/LCl mg/L COD92 mg/LFe9 mg/L Kubel15 mg/LMn1.1 mg/L SS61 mg/LABS3 mg/L CCE26 mg/L 16

CONTENTS 1.Definitions 2.Composition of Water Quality Indices 3.PRATI index 4.Reporting 17

18 REPORTING Present in understandable way, also for non- specialists (politicians). Not only Tables with data! Apply statistical tests (see lectures later) to process the data. However always keep the original data set as well. Use computer software (EXCEL, SPSS,..); use GIS to compare water quality with land use, geology...

19 Present the data in clear graphs Averages with, for example, standard errors “Box and whisker plots” (average, maximum, minimum, “percentiles”)

20 REPORTING The water quality monitoring report must show a clear structure, and be understandable Contents: - (short) summary - Introduction on the objectives of the programme - Description of the region - Different methods used - Clear presentation + analysis of the results - Conclusions and recommendations to the decision makers.