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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 trihalomethanes, 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: for
example, SI 439 of 2000 recommends that a maximum of 1 NTU "must
be strived for".
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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 oxidizable 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 Guardia must also be absent from drinking
water. These are removed by filtration and chlorination.
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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 Giardia. 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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