Drinking Water Quality Indexes A & B used by USA-EPA
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METHODOLOGICAL SHEET
DRINKING WATER QUALITY MANAGEMENT SYSTEM
Drinking Water Indexes as per Regulatory Standards applicable at 2009
Fig. A5.1 Parameters Used to build Index A
for Drinking Watyer Quality
7,7%
13,8%
3,1%
23,0%
16,9%
4,6%
3,1%
3,1%
7,7%
6,2%
3,1%
7,7%
Alkalinity
Residual Chlorine
Chlorine
E-Coli
Total Coli forms
Color
Total Hardness
Total Iron
pH
Sulfates
Total Solids
Turbidity
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Theme Variable Pressure State Impact Response Management
WATER Use and
Quality
Index A
Index B
Name: A and B Drinking Water Indexes
Descriptor: Physicochemical and bacteriological drinkable water measurement
Units: Adimensional, from 1 to 5.
Geographical
Denominator It can be measured over any water body.
Definition and
Concepts Its importance lies in compiling a high aggregated information level used to
establish whether a water is drinkable or not. The A and B Indexes are
defined as a parametrical weight of the following indicators, used by the
Environmental Ministry to measure water quality in Colombia:
1. PHYSIC QUALITY
INDICATOR UNITS ADMISIBLE VALUE
True Color PCU < 15
Odor and Flower Absent
Turbidity NTU < 5
Total Solids mg / L < 500
Conductivity µsiemens < 500
Floating substances Absent
2. CHEMICAL QUALITY
SUBSTANCE UNITS ADMISIBLE VALUE
(mg/L of) (mg/L)
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Aluminum Al+3
0,2
Antimony Sb 0,005
Arsenic As 0,05
Barium Ba 1
Boron B 0,3
2. CHEMICAL QUALITY (Continuation)
SUBSTANCE UNITS ADMISIBLE VALUE
(mg/L of) (mg/L)
Cadmium* Cd 0,005
Cyanide CN-
0,005
Chlorine Cl-
1
Cupper Cu 1
Chrome Cr+6
0,05
Phenols C6 H6 OH Absent
Oil Hydrocarbons 0,3
Total Iron Fe+3
0,3
Manganese Mn 0,1
Mercury* Hg 0,001
Molybdenum Mb 0,7
Nyquil Ni 0,02
Nitrites NO2 0,1
Nitrates NO3 46
Plate Ag+1
0,05
Lead* Pb 0,05
Insecticides 0,0001 to 0,01
Selenium Se 0,01
Active substances at
Methylene Blue ABS 0,05
Sulfates SO4
-2
250
Total Trihalo methane THMs 0,01
Zinc Zn 5
Total Alkalinity CaCO3 100
Total Acidity CaCO3 50
Residual Chlorine Cl-
0,3 < Cl-
< 10
Hydroxides CaCO3 0
Hydrogen Potential, pH Units 6,5 < pH < 9
* Highly toxic heavy metals (EU and EPA´S black list)
3. BACTERIOLOGICAL QUALITY
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SUBSTANCE UNITS ADMISIBLE VALUE
(mg/L of) (mg/L)
Total Coli forms CFU/100 ml 0*
E-Coli CFU/100 ml Negative*
*
Measured by the filtration membranes method.
Measurement Each one of the parameters can be measured by using portable laboratory
equipments manufactured by MERCK, HACH, etc. which come with the
instructions to do the titulations. In some other cases as in heavy metals,
spectrophotometer or chromatographic techniques may be used. What ever
the method or equipment employed the results must be quantitative and
they can not exceed the Allowed range or Admissible Value.
Interpretation There are some indicators which have a major influence over drinking
water quality. One economic although not 100% secure way to establish
drinkable status of water, instead running all test over the physic, chemical
and bacteriological parameters, is by calculating the A and B Indexes of
Water Quality.
Index A
The A Index is obtained from the minimal parameters to establish drinking
water quality in the Norm 2105 of the Health Ministry (Colombia, 1983),
As shown on Table A5.1 and Figure A5.1:
TABLE A5.1. Parameters and Weight for Index A*
INDICATOR WEIGHT, %
Alkalinity 7,7
Residual Chlorine 13,8
Chlorine 3,1
E-Coli 23,0
Total Coli forms 16,9
Color 4,6
Total Hardness 3,1
Total Iron 3,1
pH 7,7
Sulfates 6,2
Total Solids 3,1
Turbidity 7,7
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* Taken from CGR, “The State of the Natural Resources and the
Environment”, Bogotá, 1995, p.69.
Fig. A5.1 Parameters Used to build Index A
for Drinking Watyer Quality
7,7%
13,8%
3,1%
23,0%
16,9%
4,6%
3,1%
3,1%
7,7%
6,2%
3,1%
7,7%
Alkalinity
Residual Chlorine
Chlorine
E-Coli
Total Coli forms
Color
Total Hardness
Total Iron
pH
Sulfates
Total Solids
Turbidity
The qualification for each of the Indicators goes from 0 to 5 and it is
shown on Table A5.2
TABLE A5.2. PARAMETERS SCORES FOR INDEX A AND B*
Parameter/ SCORE 5,0 4,5 4,0 3,0 0,0
Alkalinity 0-120 > 120
Residual Chlorine 0,1-1** > 1,0
Chlorine 0-250 > 250
E-Coli 0 > 0
Total Coli forms 0 > 0
Color 0-5 > 15
Total Hardness 30-150 <30, >150
Total Iron 0-0,3 > 0,3
pH 7.0-8,5 6,5-7,0 8,5-9,0 6,0-6,5 <6 or >9
Sulfates < 500 > 500
Total Solids < 250 > 250
Turbidity 0-1 > 5
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* Source: CGR, , “The State of the Natural Resources and the Environment”, Bogotá,
1995, p.69.
** For effluent the range varies between 0,1 and 1,5: effluent concentration is higher due
to residual chlorine must be enough throughout kilometers of pipes net.
Limitations A and B Indexes varies from 1 to 5 and their result must be read as follows:
Optimal Level : 5,0
Acceptable Level: 3,0
High Risk Level : 1,0
By not including indicators such as heavy metals, their presence may be
skipped. Nevertheless they are cost-effective for continual monitoring of
freshwaters bodies over deeper monitoring analyses already have been done.
They are also useful as a first approximation, and then, in agreement with the
results, to run exhaustive research upon other physic chemical and
bacteriological parameters, already mentioned..
Alternative
Indicators Index B
The B Index uses less indicators than the A and therefore it can be built in a
more cost effective way, as shown on Table A5.3 and Figure A5.2,
Parameters and Weight for Index B. From the Parameters used to built the A
Index, shown on Table A5.1, the alkalinity is skipped due to is in a close
relationship with the pH. Chlorine, Total Iron and Total Hardness are also
skipped because they relay upon color and turbidity, as well as Sulfates and
Total Solids. Lastly, The E-Coli is not included because if it is positive, the
water must be consider as not drinkable immediately.
TABLE A5.3. Parameters and Weight for Index B *
INDICATOR WEIGHT, %
Residual Chlorine 30
Total Coli forms 40
Color 5
pH 10
Turbidity 15
* Taken from CGR, “The State of the Natural Resources
and the Environment”, Bogotá, 1995, p. 70.
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Fig. A5.2 Parameters to build Index B
for Drinking Watyer Quality
30%
40%
5%
10%
15% Residual Chlorine
Total Coli forms
Color
pH
Turbidity
Importance The Indexes A and B allows to establish drinking water quality in a quick
and cost effective way. The weight in which each parameter influences the
overall Index value, is based upon an technical criteria. For instance, Total
coliforms and residual chlorine have a major importance over drinking water
quality, while the presence of E-Coli is a determinant criteria. The
qualification system is rude, assigning “0” (zero) to the parameters that are
over the value admitted by law as shown on Table A5.2.
On the other hand, these Indexes allows an integral way for measuring water
quality, quite useful to perform comparative studies and time series, without
using 12 or 5 indicators but one single Index instead. As an example, the
results for the Indexes A and B in the city of Bogotá for the year 1994 can be
seen on Table A5.4 in the following page.
Relationship
with other
indicators The A and B Indexes of drinking water quality have a direct relation with the
simple indicators or parameters used to their construction as shown on Table
A5.1 and A5.3. They also have an indirectly relation with the DBO5 (mg/l)
and DQO (mg/l) used to measure organic and inorganic pollution,
respectively, in a water body.
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TABLE A5.4. INDEX A AND B FOR BOGOTA, 1994*
INDICATOR
VALUE Score
(A5,2)
% A
(A5.1)
Weight % B
(A5.3)
Weight
Alkalinity 18 5 7,7 0,385
Residual Chlorine 0,5 5 13,8 0,690 30 1,5
Chlorine 3,8 5 3,1 0,155
E-Coli 0 5 23,0 1,150
Total Coli forms 0 5 16,9 0,845 40 2,0
Color 9 4 4,6 0,184 5
Total Hardness 27 0 3,1 0,000
Total Iron 0,2 5 3,1 0,155
pH 7,1 5 7,7 0,385 10 0,5
Sulfates 250 5 6,2 0,310
Total Solids 120 5 3,1 0,155
Turbidity 1,8 4 7,7 0,308 15 0,6
Index Result 4,7 4,6
* Source: CGR, , “The State of the Natural Resources and the Environment”, Bogotá,
1995, p.72.
Index A show a value of 4,7, Acceptable, while Index B shows a value of
4,6, Acceptable too.
Available
Information Indicators of the Public Services Companies. Public Services
Superintendence, Bogotá. Drinking Water Regulation Commission, Bogotá.
Urban and Regional Planning Unit at National Planning Department of
Colombia, Ministry of Development, Colombia.
Bibliography Drinking Water Norm 2105, Health Ministry, Bogotá, 1983.
USA-EPA, quoted by CGR, , “The State of the Natural Resources and the
Environment”, Bogotá, 1995, p.69-72.
MMA, Drinking Water Quality Standard, Bogotá, 2008.
