Water Quality Control
 Selection of parameters for assessment
 The first priority in assessing drinking-water
quality must be to check microbiological quality.
 This can be done by measuring, at a minimum,
the “essential parameters” of
drinking-water quality: faecal coliforms (or E.
coli), and, when assessing treated water, chlorine
residual, pH and turbidity.
 Other important priorities are the aesthetic
quality of the water and contamination with
chemicals of known health risk.
 Measuring water quality
 The aesthetic quality of water, by definition, is
determined subjectively by the user.
 Microbiological and chemical testing can be made
either on-site, using field kits, or in laboratories.
 Where possible, field testing is preferred because it is
logistically much easier, and in most cases
significantly more cost effective.
 In addition, errors introduced from the preservation,
transport and storage of samples for laboratory
testing are eliminated.
 Properly trained field test kit operators can test a
large number of water sources in a relatively short
time, allowing the results to be obtained and shared
with users within hours or days.
 Microbiological analyses
 By far the most serious public health risk associated
with
drinking-water supplies
is microbial
contamination.
 Pathogens (bacteria, viruses and parasites) can cause
a wide range of health problems when ingested in
drinking water, but the primary concern is infectious
diarrhoeal disease transmitted by the faecal-oral
route.
 It is impractical to analyze water for every individual
pathogen, some of which can cause disease at very
low doses.
 Instead, since most diarrhoea-causing pathogens are
faecal in origin, it is more practical to analyze water
for indicator species that are also present in faecal
matter.
 When assessing faecal contamination, it is
recommended to measure turbidity along with E.
coli (or faecal coliforms), since pathogens can
adsorb onto suspended particles, and to some
extent be shielded from disinfection.
 When water has been disinfected, it is also
important to measure chlorine residual and pH.
 These four parameters (E. coli/faecal coliforms,
turbidity, disinfectant residual and pH) are
considered the minimum set of “essential
parameters” required to assess microbiological
quality of drinking water.
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Chemical analyses
Chemical parameters can be analyzed much more
rapidly than microbiological ones, because there
is no need for incubation.
Most parameters must be analyzed in a
laboratory, at least for quantitative results.
Some parameters, though, might change during
storage and transport (e.g., pH) and should be
measured at the sampling site.
Inexpensive field kits are available for semiquantitative determination of many parameters,
and in some cases sophisticated equipment can be
made portable for field analysis.
 Precision and accuracy
 In all experimental measurements, there is a degree of
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uncertainty or error.
When reporting data, the degree of uncertainty can be measured
by considering the precision and accuracy of the analysis.
The precision simply means the reproducibility of the analysis:
if the same sample is analyzed multiple times, how much will
the results vary?
Accuracy, on the other hand, refers to how close the
measurement is to the true value.
Analytical precision can be assessed by making repeat
measurements and calculating the ratio of the standard deviation
to the average.
This is called the coefficient of variation, and as a rule of thumb
should be less than 10% for laboratory measurements.
Precision will depend primarily upon the instrument and method,
but also on the operator and quality control procedures.
Preventing Contamination
 Contamination prevention is a two-pronged
process:
1- Reducing the amount of pollution entering the
environment as a whole
2- Erecting barriers to prevent any contamination
that is present in the environment from reaching
water supplies.
 Sources and pathways of contamination
 No natural water is absolutely pure – the chemical
and physical characteristics of water are constantly
changing through interaction with the environment.
 These changes can be positive: water is purified as its
percolates down to aquifers and some adsorbed
minerals can improve the taste and perceived value
of water.
 Sometimes the changes can result in water that
remains safe, but is unacceptable to consumers for
aesthetic reasons (taste, smell or colour).
 And in some cases water can become unsafe for
human consumption through contamination by
naturally occurring chemicals (such as arsenic) or
through pollution from human activities (such as
pesticides).
 Sources and pathways of chemical contamination
 There are two sources of chemical contamination:
1) Naturally occurring chemicals
2) Anthropogenic (caused by human activity) pollutants.
 There are several naturally occurring chemical compounds that
pose a threat to human health, the most serious being arsenic and
fluoride.
 Other natural chemicals affect the aesthetic quality of water and
cause health problems indirectly by forcing people to use
alternative sources that may be less safe. Iron is the most
common such contaminant.
 Groundwater sources are typically the most affected by natural
chemical contamination although there are cases of seriously
contaminated surface water as well.
 In these cases, the chemical contaminant is present in the rocks
and soils of the aquifer and is absorbed by the groundwater
through a variety of chemical processes.
 Natural chemical contaminants often affect large areas
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and multiple water sources, although there may be
significant variation in contamination levels from source
to source.
Arsenic contamination levels, for example, are highly
variable due to the complexity of the affected aquifers
and the chemical processes involved.
The level of contamination may also be influenced by the
depth of the water source and whether or not it is capped.
In general, natural contamination cannot be prevented.
If an aquifer is affected, the only remedial measure is to
tap another, unaffected aquifer (e.g., a deeper aquifer),
use another source such as surface water or use filters or
other treatment measures to remove the contaminant
from the pumped water.
 In addition, there are techniques that can improve the
water quality in situ, in the aquifer itself. This
involves reducing the contamination concentration
levels through dilution by injecting uncontaminated
water into the aquifer, or by inducing a chemical
state in the aquifer that minimizes the adsorption of
the contaminant in the water.
 These techniques are in general not fully developed,
and used on a limited basis.
 Pollutants are harmful chemicals released into the
environment from agricultural activities, industrial
processes and household wastes.
 There are two types of pollution:
1) point source (such as effluents from factories)
2) non-point source (including run-off from fields
and emissions of chemicals into the atmosphere.)
 All types of water sources can be affected by
pollution.
 Groundwater is contaminated though seepage from
non-point source pollutants and from point sources
such as leaking chemical storage tanks.
 Surface water is often contaminated through the
release of industrial and domestic effluents directly
into lakes and rivers, and from pesticide run-off from
fields.
 Even harvested rainwater is sometimes at risk: rain
can absorb and retain contaminates from air
pollution, especially near certain types of industries.
 Pollution, especially point source pollution, can be
prevented, as it is easier to identify and isolate.
Pathways for faecal contamination of water
sources
 Faeces are the most serious water contaminant
affecting people’s health and the interruption of the
fecal-oral cycle is the key objective of most water
and sanitation programmes in developing countries.
 Both animal and human faeces are health threats;
however human faeces are generally the most
dangerous.
 There are other sources of microbiological
contamination besides faeces, but because faeces are
by far the most common and the most dangerous, this
section focuses on faecal contamination pathways.
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 Pathways for faecal contamination during
transport and storage
 Protected water sources do not ensure that water used
for drinking and cooking in the home is safe.
 Household water storage (a practice common in
developing countries) contributes to drinking-water
contamination.
 Water stored in homes is often faecally contaminated
at levels far above the contamination level at the
source.
 Studies show that water stored in homes routinely
have faecal coliform levels hundreds of times higher
than is present in the source – some studies have
documented thousand-fold increases in faecal
coliforms.
 There are three reasons water quality deteriorates
during the storage and transport of water:
1- Poor hygiene knowledge prevents people from
taking basic steps to minimize contamination
2- Inadequate household latrines, hand-washing
facilities and poor community environmental
sanitation results in more faeces in and around
households
3- commonly used transport and storage containers
are easily contaminated.