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Frequently Asked Question's
Drinking Water Quality:
Q1: Why does my drinking water have a bad odour/taste?
Odour and tastes in drinking water can
derive from several sources such as chlorine, organic
matter (such as decaying leaves and algae), dissolved
gases, industrial discharge, especially phenols. These
parameters are the source of complaints from customers
and can be removed by using carbon treatment in conjunction
with ozone. The test is carried out in the laboratory
normally on raw water by continued dilution of the odouriferous
water until the odour/taste disappears. There is no
specification for drinking water other than acceptance
by consumers: taste and odour complaints by consumers
must be investigated by the water provider. Chlorination
of raw water to remove bacteria and viruses causes chlorine-type
odours. The presence of organic matter in surface water,
which has not been removed in the treatment processes
can cause bad odours and confer an objectionable taste
in the water. The removal of organic material from the
raw water by filtration and carbon treatment reduces
these unpleasant odours and tastes. Reverse osmosis
is also very effective in removing odours, tastes and
colour from drinking water. Treatment of the water with
UV or ozone instead of chlorine will also make the water
more palatable.
Where cryptosporidium or giardia is suspected,
1-micron (absolute) filters are recommended.
The presence of trihalomethenes, which
may result from the chlorination of low-grade water
poses a threat to the health of the consumer. Carbon
treatment will remove these substances as well as odour
and taste-causing materials.
Usually water with bad odours and tastes
will also be coloured.
'Rotten egg' type odours may also arise
where groundwater is being used as the raw water source.
These are due to volatile sulphides, which are produced
by bacteria in deep bores. These anaerobic bacteria
break down sulphates giving rise to hydrogen sulphide.
The acidity or basic nature of water is
expressed as the pH. It is important that the pH value
be as close to 7.0 as possible in order to reduce the
corrosivity of water and to limit its hardness and alkalinity.
The regulations stipulate a range: 6.5 - 8.5 pH units.
Interestingly, the toxicity of some substances in water
can depend on the pH. For example, at a pH of 4.8, iron
at 4.0 mg/L is not toxic to fish, however, if the pH
is 5.5 then iron levels of 0.9 mg/L can cause fish kills.
Some natural waters (where the soil is peaty) have pH
values below or close to 6.0 with the result that pH
adjustment will be required if the source is to be used
for abstraction of drinking water. If the pH of water
is low then it will cause corrosion to metal pipe work
and introduce toxic metals into the supply. It is also
important to realise that chlorine (rather hypochlorous
acid) is a much more effective as a disinfectant if
the pH is low. For instance at a pH of 8.0 the hypochlorous
acid is present at 20% whereas at a pH of 7.0 the hypochlorous
acid is now at 70% approx. Also, pH affects suspended
solids removal from water. The lower the pH the better
the flocculation will be and hence the filtration process
will be more effective.
Q3: What is turbidity and what
causes it?
Turbidity is a measure of how clear water
is. The units of measure are NTU's (Nephelometric Turbidity
Units). The lower the NTU of a sample of water the clearer
the water is. The recommended value for drinking water:
0.5 NTU's. The higher the level of suspended solids
in the water the higher the turbidity will be. The presence
of pathogens such as Cryptosporidium and Giardia in
surface water can cause turbidity and hence the need
to maintain your supply at or below 0.5 NTU or less
to protect your customers against these pathogens: SI
439 of 2000 recommends that a maximum of 1 NTU "must
be strived for".
| Q4: What is
chlorination and why is it necessary? |
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Common disinfectants are chlorine, ozone
and UV. Chlorine is added to drinking water and leisure
water in the form of chlorine gas, sodium hypochlorite,
calcium hypochlorite or other Chlorine-containing disinfectants
such as chlorine dioxide, to act as a germicide/biocide
in order to remove harmful organisms such as bacteria,
viruses, and cysts which may be in the water. As well
as its effects as a germicide, chlorine will have other
effects as well, causing insoluble oxides of iron and
manganese to form in the water should the water contain
soluble iron and manganese. In combination with organic
material such as algal blooms, and especially with humic
acid, trihalomethanes (THM'S) can also be formed: some
of these are suspected carcinogens. Chlorine is not
that effective in removing cysts from drinking water.
Filtration is also needed.
The lower the pH and the higher the temperature
of the water the more effective the disinfection power
of chlorine disinfectants is. It is recommended that
the residual chlorine in the distribution network be
maintained at 0.1 to 0.3 mg/L chlorine as residual free
chlorine. The effectiveness of the disinfection process
is determined by a number of variables such as pH, water
temperature, concentration of the chlorine injected,
how good the mixing is, contact time and the amount
of oxidisable matter present in the water. The World
Health Organisation (WHO) has set as a guide level for
effective chlorination, a residual free chlorine (RFC)
value of 0.5 mg/L after 30 minutes contact. Viruses
and cysts such as Cryptosporidium parvum, Giardia lamblia,
Entamoeba histolytica, can be difficult to inactivate
and it is therefore important to have effective contact
time with the disinfectant so as to ensure protection
of consumers at all times. Filtration is the most effective
way of ensuring cysts do not enter the network.
Chlorination is effective if hypochlorous
acid is present in the water and must be present as
'free chlorine' at points of use at about 0.20 mg/L
as recommended by the World Health Organisation. The
total chlorine can also be measured and the difference
between 'free chlorine' and total chlorine indicates
the level of pollution present prior to chlorination.
Health and Safety Issues:
Ingestion of sodium hypochlorite will
burn the mouth and digestive tract. Sodium hypochlorite
contact with the skin will also cause burns. Wear
suitable personal protective equipment when handling
chlorine disinfection products. Antidote:
Bread-soda in water.
Note on the stability of
sodium hypochlorite solutions: Sodium hypochlorite
is available in solution form as 11%(w/v) sodium hypochlorite
or 15% (w/v) sodium hypochlorite. These should be
kept cool and in the dark. In sunlight these solutions
will lose concentration at a rate of 3-4 percentage
points per month. Even when held in the dark at 9
Celsius, the solution strength will drop by over 1
percentage point in a month.
Q5: What is Ozonation?
Ozone, a relative of oxygen, is also a
powerful disinfectant. Its activity matches chlorine
and essentially behaves in the same way, though there
are no risks from THM formation with ozone as there
is with the use of chlorine. The advantages are that
the method removes taste and odour, improves palatability,
oxidises iron, manganese, and organics, and is less
sensitive to pH changes. It is also very effective against
Cryptosporidium and as a disinfectant it is very powerful.
The disadvantages are that it requires skilled maintenance
input, it is expensive and unfortunately provides no
disinfectant residual, thereby necessitating post treatment
chlorination.
Nitrate derives from the oxidation of
ammonia in the environment and also from agricultural
nitrate fertiliser run-off. Drinking water contaminated
with nitrate or nitrite can be hazardous to infants
above 11.3 mg/L N(or 50 mg/LNO3-)
giving rise to the so-called 'blue baby' syndrome (Methaemoglobinaemia).
This condition has its origins in nitrite ingestion
rather than nitrate. The nitrate is reduced in the body
to nitrite, which in turn reacts with blood haemoglobin
to induce the syndrome. The presence of nitrite in water
sources above about 0.03mg/L indicates pollution. These
parameters should be monitored regularly.
Q7: How do I know that the
water is safe to drink?
There are several quality indicators of
suitability for the purpose, broadly divided into two:
1. Chemical parameters:
The presence of heavy metals, ammonium,
nitrate, aluminium, etc can indicate that the water
is unsuitable for consumption. (See audit monitoring
and check monitoring)
2. Biological:
a:
General Coliforms: The presence of general coliforms
in drinking water indicates that disinfection is
not occurring or there is contamination post disinfection.
These organisms are harmless: they merely indicate
a potential problem.
b: E. Coli: Should E. Coli be present in
the water sample then there is an issue requiring
urgent attention. In order to ensure that consumers
are protected from hazardous micro-organisms such
as E.Coli 0157, a disinfectant such as chlorine
or ozone must be added to water, usually following
filtration, at about 2.0-4.0 mg/L. It is estimated
that E.Coli 0157 is present in 10-15% of the Irish
cattle herd. The organism can be fatal if ingested.
c: Enterococci: The presence
of these organisms again indicates that the source
is contaminated with faecal material.
d: Cryptosporidium and giardia
must also be absent from drinking water. These are
removed by filtration and chlorination.
| Q8: How can
I guarantee that my drinking water is safe? |
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There are no guarantees! All one can do
is minimise risks to health.
1. Ask the water provider to
present you with a copy of the water quality data
obtained for the supply. Data for raw water as well
as data for treated water would be of value.
2. A managed point of use treatment, is also
a good way of ensuring that your water is meeting
your requirements. There are a number of these systems
available, from very simple treatment using particle
filters to more sophisticated systems using reverse
osmosis.
Reverse osmosis (RO) reduces
significantly (normally >95%) the levels of contaminants,
which may be in drinking water whether these are biological
or chemical. As an indicator of the power of the technique,
the conductivity of the water can be reduced significantly.
The recommended arrangement is to use particle filters
down to 1 micron in conjunction with carbon filters
to further remove contaminants before the water is
eventually passed through the RO membrane. Typically,
total dissolved solids can be reduced from 200 mg/L
to less than 20 mg/L when the process is applied.
These are normally fitted under the sink in the kitchen
and are easy to fit. The can provide up six
purification stages. RO is very effective against
cryptosporidium.
Q9: What is cryptosporidiosis?
Cryptosporidiosis is a diarrhoeal disease
caused by microscopic parasites of the genus Cryptosporidium.
Once an animal or person is infected, the parasite lives
in the intestine and passes in the stool. The parasite
is protected by an outer shell that allows it to survive
outside the body for long periods of time and makes
it very resistant to chlorine-based disinfectants. Both
the disease and the parasite are commonly known as "crypto."
The parasite can be removed using reverse osmosis or
by using filters which are 1 micron absolute. The parasite
is not readily controlled by chlorine or ozone.
Q10: What are the symptoms of
cryptosporidiosis?
The most common symptom of cryptosporidiosis
is watery diarrhoea. Other symptoms include:
- Dehydration
- Weight loss
- Stomach cramps or pain
- Fever
- Nausea
- Vomiting
Some people with crypto will have no symptoms
at all. While the small intestine is the site most commonly
affected , Cryptosporidium infections could possibly
affect other areas of the digestive or the respiratory
tract.
Q1: What chemicals does leisure water
contain?
Chemicals are used to disinfect water,
which can become contaminated with micro-organisms carried
by the users of the leisure water facilities. The water
will contain chlorine (or hypochlorite), chlorine by-products
such as chloramines, sulphates derived from acid dosing.
Q2: Why is acid added?
The acid controls the pH where the water
contains lime of where calcium hypochlorite is used
as a disinfectant. The pH is normally controlled between
7.2 and 7.6 pH units. Chlorine is less effective at
higher pH: its killing power diminishes with rising
pH.
Q3: What are the main hazards associated
with leisure water?
Where there is poor control of disinfectant
such as chlorine/ozone, micro-organisms will survive
because there will be adequate amounts of food to sustain
life in the leisure water. The main threats are presented
by E. Coli, pseudomonas (earache and throat infections)
and Staphylococcus aureus (ear, nose and throat infections).
Maintaining the chlorine levels between 1 and 2 mg/L
will kill most organisms but not cysts such as cryptosporidium
or guardia. These latter parasites are removed by efficient
filtration systems.
Over chlorination can cause eyes to weep
and high alkalinity can irritate the skin.
Q4: What about legionnaires and leisure
water?
Where there is poor control of chlorine
dosing legionnaires disease can strike. The organism,
legionella, is responsible and survives in stagnant
water, which contains sufficient food to sustain growth.
Breathing vapour with legionella will almost certainly
cause serious illness and could be fatal. There have
been several cases of the disease recorded which resulted
in serious illness or death. Smokers and the immunocompromised
are most at risk. Showers can also present a problem.
These should be managed so that water is not allowed
to stagnate in supply tanks, pipelines and shower heads.
Q1: What is wastewater/effluent?
There are two types, treated and untreated
(raw effluent).
Effluent is also known as wastewater and
is generated by each of us daily and also by industry.
Because it is wastewater it may be hazardous and will
almost certainly contain micro-organisms.
Because effluent contains food and micro-organisms
and possibly other contaminants it will harm the environment
if untreated. Raw (untreated) effluent can be extremely
damaging and must not be allowed into groundwater, seas,
estuaries, rivers or lakes.
However, the potency of the wastewater
can be reduced by allowing the food in the waste to
be consumed in air (activated sludge treatment) or in
the absence of air - anaerobic digestion.
Q2: What is BOD?
The BOD is a measure of the food
quantity present and hence the polluting strength of
the wastewater. The higher the BOD the more damaging
the wastewater and the more likely the risk of fish
kills.
COD and TOC, like BOD indicate the polluting strength
of the wastewater.
Q3: Is effluent dangerous?
Yes if ingested. When handling effluent
one should wear gloves.
Q4: What's in treated wastewater?
The composition of treated wastewater
can vary but broadly speaking there will be solids (dissolved
and insoluble or suspended solids), some food and nutrients
such as phosphate, nitrate and ammonium.
If the wastewater is from chemical
industry, traces of solvents , heavy metals, phenols etc
and the like may be present. These will be controlled
by licence and breaches will incur penalties from the
EPA or the county council.
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