Parameters Tested, Significance and Limits
Introduction
The classification of a water as potable (fit for drinking) or otherwise is based on the
requirements of the European Communities (Drinking Water) (No 2) Regulations
2007 (S.I. No. 278 0f 2007). The Drinking Water Regulations cover a total of 48
bacteriological, chemical and physical parameters for most of which the concentration
limit or parametric value is specified.
The bacteriological tests are very important in assessing the safety of drinking water
and tests for indicator organisms such as E.coli are carried out routinely on all
samples. All public supplies are chlorinated in order to ensure that the drinking water
is safe. Free chlorine is measured when taking each sample.
Routine chemical and physical tests are also carried out such as tests for Aluminium,
Colour, Conductivity, Iron and Nitrite. Some further tests will depend on whether the
source is groundwater or surface water. Water Hardness is not on the list but is tested
on groundwater samples occasionally for information to the consumer.
Total Coliforms, E.coli and Enterococci
In order to ensure a high factor of drinking water safety simple routine tests were
devised to test for bacteria in water. The bacteria types chosen are called indicator
organisms. The universal indicator organisms used are Total coliforms and
Escherichia Coli. The routine positive identification of pathogenic bacteria is difficult.
The indicator bacteria by definition, are (a) easily detected and identified, (b) of the
same origin as the pathogens (i.e. from the human or animal intestine), (c) present in
far greater numbers than the pathogens, (d) present whenever the pathogens are likely
to be present and (e) able to show the same or better survival characteristics than the
pathogens and they must not be in themselves pathogenic (disease causing).
E.coli and Enterococci bacteria are of faecal origin (human and animal) and are
excreted in the vast numbers and widely distributed in nature. Their presence in a
water supply is an indication of the risk that pathogens may be present. There are
many sub types of E.coli and Enterococci only some of which are pathogenic. The
absence of E.coli indicates strongly the probability that pathogens are absent.
Total coliforms include E.coli bacteria and also other bacteria with similar properties
which originate in soil and are non-faecal. The presence of Total coliforms in the
absence of E.coli in a water supply generally indicates a lack of chlorine in the water
or contamination at the tap.
The 2007 Regulations set the parametric value for E. coli and Enterococci at 0/100ml.
Aluminium
Aluminium sulphate is widely used for colour and particle removal in the treatment of
surface waters for drinking. The World Health Organisation (WHO) in summary
suggests that human exposure to aluminium may occur through a variety of routes,
with drinking water probably contribution less than 5% of the total intake. Aluminium
is used in the treatment of the surface water sourced supplies only i.e. Poulaphouca
Regional, Leixlip Regional and N Carlow S Kildare Regional.
There has been no exceedance of the aluminium limit in 2012.
The 2007 Regulations set the parametric value of Aluminium at 200µg/l.
Fluoride
Water Fluoridation is public health policy in Ireland to aid in the prevention and
management of tooth decay. Fluoridation began in Ireland in 1964 in accordance with
the Health (Fluoridation of Water Supplies) Act 1960. The Act provides that health
authorities arrange for the fluoridation of public water supplies, and that local
authorities act as their agents.
This policy was the subject of a major review in 2000. The Forum on Fluoridation,
established by the Minister for Health and Children in 2000, reviewed the fluoridation
of public water supplies. The main conclusion of the Report of the Forum on
Fluoridation 2002 was that the fluoridation of public piped water supplies should
continue as a public health measure.
The Fluoridation of Water Supplies Regulations 2007 sets the fluoride level at
between 0.6-0.8mg/litre (equal to 0.6-0.8 parts per million). The level of fluoride in
toothpaste can be up to 1500mg/kilo.
Currently the Irish Expert Body on Fluoridation deals with queries on fluoridation.
“The Irish Expert Body is of the opinion that there continues to be overwhelming
evidence that water fluoridation significantly benefits dental health. The Expert Body
is satisfied, having studied current peer reviewed scientific evidence worldwide, that
water fluoridation, at the optimal level, does not cause any ill effects and continues to
be safe and effective in protecting the oral health of all age groups.” A major
advantage in favour of water fluoridation is that the dental health benefit reaches
disadvantaged children.
Co Kildare
Rathangan and Monasterevin supplies are fluoridated by Kildare Co Co. The
Regional supplies which supply most of the population in Kildare are also fluoridated.
There has been no exceedance of the fluoride limit in 2012.
The 2007 Regulations set the parametric value between 0.6-0.8mg/l.
Iron
Iron is present in significant amounts in soils and rocks, principally in insoluble
forms. However, soluble forms of iron can be present in groundwater sourced in some
geological formations. Problems with iron in drinking water are aesthetic rather than
health related. However in some groundwater sources, as in many wells in Co.
Kildare, it is a nuisance. Excess iron in water results in a brown colour and an
increase in turbidity. Iron precipitates out on aeration and causes brown/rust coloured
deposits. Iron enriched water will taste “earthy” and when used to make tea may react
with tannins giving rise to off-colours.
Iron, along with manganese, is an abundant naturally-occurring metal which can exist
in soluble and insoluble states. However when iron occurs in the treated surface water
public supplies it almost invariable arises from cast iron mains in the distribution
systems.
The 2007 Regulations set the parametric value at 0.200µg/l.
Manganese
As with iron, manganese is found widely in soil and is a constituent of many ground
waters in Co Kildare. Similar to iron it may be brought into solution in reducing
conditions and the excess manganese may be later deposited in a black sludge or
black flecks when the water is aerated. The objections to excess manganese, in
common with iron, are aesthetic due to black deposits and taste problems. The WHO
revised its provisional health-based guideline value to 0.4 mg/l (400µg/1)
The 2007 Regulations set the parametric value at 50µg/l.
Nitrates
Relatively little of the nitrate content found in natural waters is of mineral origin,
most coming from organic and inorganic sources. Organic sources include animal and
human waste and the main inorganic source is artificial fertiliser. It is very important
to maintain septic tank and other sewage treatment systems in working order.
However, bacterial oxidation and fixing of nitrogen by plants can also produce
nitrates naturally.
High levels of nitrate in drinking water are unsuitable for infants as such water may
induce the “blue baby” syndrome (methaemoglobinaemia). The nitrate itself is not a
direct toxicant but is a health hazard because of its conversion to nitrite which reacts
with blood haemoglobin to cause methaemoglobinaemia.
The presence of nitrate in ground waters is a cause for suspicion of sewage pollution
or of excess levels of fertilisers or excess manure slurries spread on land.
The 2007 Regulations set the parametric value at 50 mg/l.
Typical Nitrate Results for major Water Supplies serving Co Kildare
Supply
Nitrate
Type
Poulaphouca Regional
<6.64
Surface water
Leixlip Regional
< 15.0 to <6.64
Surface water
N Carlow S Kildare Regional
<6.64 to 14
Surface water
Athy Town Council
19 to 32
Groundwater
Monasterevin
<10
Groundwater
Rathangan
<15
Groundwater
Nitrite
Nitrites exist normally in very low concentrations in water. Nitrite is an intermediate
stage in the oxidation of ammonia to nitrate, and this process can take place in soil.
Sewage is a rich source of ammonia nitrogen, and as such waters which show an
appreciable amount of nitrite are regarded as being of questionable quality and
contamination with sewage may be suspected.
The 2007 Regulations set the parametric value at 0.5mg/l (NO2) in the distribution
system.
Ammonium
Ammonia is generally present in natural waters, in small amounts, as a result of
microbiological activity which causes the reduction of nitrogen-containing
compounds. Note: In acid bog water the level of ammonia can be elevated in the
absence of pollution.
The 2007 Regulations set the parametric value of Ammonia (NH4) at 0.3mg/l.
Odour and Taste
Odour and taste are often related. A strong odour or taste from drinking water for
consumption may cause rejection on the part of the consumer. The majority of odour
and taste complaints arise from the presence of chlorine in the waters delivered to
consumers. Chlorine concentrations in drinking water, even when in excess, are not a
direct hazard to the consumer. The World Health Organisation has issued a guideline
value of 5mg/l for chlorine in drinking water. The normal level of chlorine in drinking
water is less than 0.5mg/l.
Odour/taste complaints can also be due to contamination, the presence of small traces
of phenols, decaying vegetation in source water, metals such as copper etc.
Trihalomethanes
Chlorine is the most important chemical used in water treatment. Chlorine in a dilute
solution is a most effective agent for the disinfection of water. It is very efficient at
destroying bacteria and keeping the water in the distribution system safe.
Chlorine is a strong oxidising agent and can combine with organic matter in the
source water to form trihalomethane compounds one of which is chloroform. Source
waters are treated so that colour and organic matter present are removed prior to
chlorination and this reduces the formation of trihalomethanes. See trihalomethane
test results 2010 and 2011.
The 2007 Regulations set the parametric value for Total Trihalomethanes at 100µg/l.
Turbidity
Turbidity in water arises for many reasons. Sediment can precipitate out from hard
water or from water containing iron and manganese. Sometimes silt, fine clay, or
sand can pass through from the water treatment plant and be deposited in the mains.
Silt may be disturbed in the mains supply due to interruptions to supply, bursts, low
pressure, etcetera and this may result in turbid water at the tap. The existence of
turbidity in water will affect its acceptability to consumers and it will also affect use
in certain industries.
There is no parametric value set for Turbidity other than that the water “be acceptable
to consumers”.
Cryptosporidium
Cryptosporidium is a microscopic protozoan parasite, which may occur in the
intestinal tract of humans and animals. It can cause disease in both children and adults
called cryptosporidiosis. Cryptosporidiosis can cause fever, stomach upsets, weight
loss and diarrhoea and is serious for those with weakened immune systems.
Cryptosporidium is protected by an outer shell (cyst) permitting it to survive long
periods in the environment. The cyst only multiplies in the body. The cyst is not
destroyed by chlorine, although it is killed by boiling water. Ultra violet treatment of
drinking water also inactivates the cyst. The cysts are generally effectively removed
in association with colour and turbidity water treatment. The Regional supplies
serving Co. Kildare are all sourced from surface waters and these waters are tested
regularly for Cryptosporidium with satisfactory results.
Outbreaks of cryptosporidiosis caused by its presence in drinking water have been
reported in Ireland. Outbreaks are also significantly associated with person to person
spread and use of recreational water.
There are no standards in current Irish legislation concerning Cryptosporidium in
drinking water. Risk assessments are carried out on sources and catchments in order
to reduce risk of cryptosporidium.
Test Results: Cryptosporidium is tested at the Water Treatment Plants supplying the
Regional supplies all three of which are sourced from surface waters. There was no
exceedance of public health significance to date in 2012. The ground waters serving
the Co. Kildare supplies are not at risk with regard to Cryptosporidium and therefore
are not tested.
Lead
See Lead Test results 2012 and 2011 and explanation of Parameter.