Water quality in Northern Ireland is improving because of increased investment in pipes and treatment works, a report has said.

More than 99% of drinking water is of good enough standard, the Drinking Water Inspectorate annual report for 2008 added.

Regional Development Minister Conor Murphy said: “While the standard of public drinking water here is good, and continues to get better, we recognise there is still room for improvement.”

Yesterday's dossier also said cases of reduced drinking water quality in Northern Ireland were on the increase because of treatment difficulties.

The Inspectorate expressed concern after 29 instances were recorded of deteriorated standards in 2008.

Acting chief inspector Margaret Herron said nearly half involved treatment difficulties.

“It is important that NI Water continues to learn from these incidents and that sufficient priority is given to maintaining and improving, where necessary, the fundamental parts of the water treatment processes, including maintenance of equipment and robust operating procedures,” she said.

Of the 29 incidents 14 (48%) involved treatment difficulties at seven water treatment works which led to too much aluminium and six were attributed to inadequate disinfection with some requiring boil water notices, the Inspectorate's annual report said.

Overall drinking water quality, which includes results of tests carried out at water treatment works, service reservoirs and consumers' taps, continues to get better with 99.69% compliance in 2008.

Improvements were down to a variety of capital infrastructure projects. Overall microbiological quality remains high at 99.84%.

NIW director of asset management George Butler said they were delivering the best quality drinking water ever.

“While we are very encouraged by these positive results, NIW is committed to continuing with its programme of work,” he said.

“A major £110 million capital investment programme under a Public Private Partnership contract has recently been completed, providing a more effective treatment regime which has led to increased regulatory compliance.”