The Drinking Water Inspectorate for Northern Ireland has published the 12th Drinking Water Quality Report - the first since the Inspectorate became a statutorily appointed body in April 2007, under the Water Reform process, and the fourth since new Regulations for public drinking water supplies came into operation in January 2004.

The Report says that overall compliance with European and national drinking water quality standards for all test results has improved from 98.89% in 1996, to 99.60% in 2007. However, the report highlights water quality issues where compliance with the regulatory standards still has to be achieved.

The Inspectorate says that more improvement work remains to be done and that in addition to achieving improved compliance, it is important for Northern Ireland Water Ltd (NI Water - the sole supplier of public water in Northern Ireland) to maintain and effectively operate its existing assets. During 2007, the Inspectorate noted deterioration in water quality supplied from some older treatment works and took enforcement action to ensure that drinking water quality from these works is maintained in the remaining period of their operation, before replacement works come on line.

The Report states that overall microbiological quality has shown a significant improvement at 99.85% compliance compared with 99.76% achieved last year. There was a significant increase in the number of tests taken from service reservoirs meeting the regulatory standards in 2007, as well as increased compliance at water treatment works and at consumers’ taps. Drinking water quality at consumers’ taps is assessed using ‘mean zonal compliance’, an index which is calculated using 40 parameters from the regulatory sampling programme. In this reporting year, 13 parameters failed to achieve full compliance: trihalomethanes (THMs), iron, aluminium, lead, manganese, pesticides, total pesticides, turbidity, E. coli, nickel, heptachlor epoxide, colour, and hydrogen ion.

Compared with last year, there has been a decrease in the compliance achieved at consumers’ taps: 99.34% reported for 2006; and 99.30% reported for 2007. The Inspectorate says that this is mainly due to the significant increased number of THM contraventions and that it is disappointing to note this particular deterioration as there had been a progressively upward trend for THMs: from 68.44% in 2004, 75.37% in 2005 and 83.04% in 2006 to this lower value of 79.37% in 2007. The Report says that NI Water gave the principal reason for this to be due to changes in raw water quality caused by heavy rain.

The Inspectorate has emphasized to NI Water the importance of water treatment processes being robust enough to deal with the changing raw water quality: capable of removing organic matter from the raw water and, hence, reducing THMs in the distribution system. The Report says that the completion of new and upgraded water treatment works by 2009, together with careful operational management of the water treatment works and distribution systems, should significantly progress THM compliance. The inspectorate is also anticipating improvements in lead and pesticide compliance in future years as a result of work currently under way.

During 2007, 20 incidents and eight events relating to water quality were notified to the Inspectorate, twelve of which related to situations of compromised disinfection, six related to treatment difficulties and two were caused by other factors. The Report states that the development of a drinking water safety plan approach is seen by the Inspectorate as an effective way of mitigating risks of contamination in the water supply chain, from the source waters in the catchments, through the water treatment works and onwards through the storage and distribution networks to consumers’ taps.

http://www.ni-environment.gov.uk/other-index/drinking_water_quality_in_northern_ireland_2007.pdf