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The most important health indicators of drinking
water are the microbiological parameters, in particular
Escherichia coli (E. coli)
bacteria. The presence of
E. coli
in drinking water indicates either that the disinfection
process at the water treatment plant is not operating
adequately or that faecal contamination has entered
the water distribution system after treatment. As shown
in Figure 8.4, the incidence of
E. coli
in public water
supplies in Ireland continues to decrease. However, the
microbiological quality of private water supplies remains
inferior to public supplies, with a significant number of
E. coli
detections in small private supplies and private
group water schemes. Furthermore, it is estimated that
up to 30% of the 170,000 unregulated private wells
in the country are contaminated with
E. coli
, which
presents a health risk for those consuming the water
(EPA, 2015c).
There have been cases of faecal-derived
Cryptosporidium
contamination of public water supplies in Ireland leading
to illness in the community, e.g. Galway City in 2007 and
Westport in 2015. These outbreaks highlight the risks to
health associated with the abstraction of drinking water
from poorly protected sources, and the need for modern
and well-managed water treatment systems. Figure 8.5
shows the number of cases of cryptosporidiosis reported
in Ireland between 2004 and 2015 (HPSC, 2015). There
were 439 cases of cryptosporidiosis in 2015, 10 of which
were definitively associated with drinking water supplies
(eight confirmed cases in a general outbreak in Westport
and two confirmed cases in a family outbreak linked to a
private well).
The winter storms in late 2015/early 2016 resulted in a
considerable increase in the number of consumers on Boil
Water Notices across the country as a result of a number
of supplies becoming contaminated with
Cryptosporidium
because of inadequate barriers at water treatment plants.
As guided by the EPA, Irish Water is adopting the Water
Safety Plan approach to managing drinking water supplies.
This involves a holistic process to identify, reduce and
manage risk, and thereby improve the resilience of water
supplies. This should result in a reduced risk to public
health of drinking water contamination.
Figure 8.5
Annual Number of Cryptosporidiosis Cases in Ireland, 2004‑2015 (Source: HPSC, 2015)
0
100
200
300
400
500
600
700
2015
2014
2013
2012
2011
2010
2009
2008
2007
2006
2005
2004
439
394
514
556
428
294
445
415
608
369
568
425
Number of cases
Figure 8.4
Number of Public Water Supplies in which
E. coli
was Detected in Compliance Monitoring,
2005‑2014 (Source: EPA, 2015c)
0
20
40
60
80
100
2014
2013
2012
2011
2010
2009
2008
2007*
2006
2005
8
10
7
12
20
27
39
52
77
87
No. of PWS with E.coli detections
* EPA became supervisory authority for PWS with enforcement powers