In Ireland, most drinking water originates from surface water (i.e. rivers and lakes). This is particularly so for public water supplies, whereas group water schemes and small private supplies tend to be slightly more reliant on groundwater or spring water. The most important indicators of drinking water quality in Ireland are the microbiological parameters and, in particular, E. coli. E. coli is present in very high numbers in human or animal faeces and is rarely found in the absence of faecal pollution. As such its presence in drinking water is a good indication that either the source of treatment plant is not operating adequately. E. coli is not itself a harmful organism but indicates that harmful organisms may be present.
Drinking water is regulated by the European Communities (Drinking Water) Regulations, 2000. Under this legislation there are two microbiological, 26 chemical and 20 indicator standards that must be adhered to. More stringent standards will apply in 2008 for two chemical parameters, the current level of 25 m g/l for bromate will fall to 10 m g/l and the current level of 150 m g/l for trihalomethanes will fall to 100 m g/l. In 2013 the current level of 25 m g/l for lead will fall to 10 m g/l.
In 2005 the majority of the E. coli exceedances were moderate (<20 cfu/100ml) and one-off: they were not detected in follow-up samples. The majority of exceedances in public water supplies (those that serve 80 per cent of the population) were found in the smaller supplies. The rate of compliance in the large public water supplies (serving more than 5,000 people) was 99.8 per cent in 2005 compared with 98.7% in 2003.
The quality of group water schemes has historically been inferior to that of the public water supplies. It was always understood that the private group water schemes were the main cause of concern in the group water scheme sector. The rate of compliance in the private group water schemes was 77.5 per cent in 2005 compared with 74.9 per cent and 78.1 per cent in 2003 and 2004 respectively.
The poor microbiological quality of the private group water schemes is the most challenging issue facing the authorities charged with responsibility for drinking water in Ireland. Though the majority of these schemes have plans in place to be upgraded as part of a Design Build Operate (DBO) bundle, there are a significant number of poor-quality schemes which are not participating in this process.
