A report by the Environmental Protection Agency (EPA) states that public drinking water supplies in Ireland now have similar compliance levels for the E.coli bacteria to those in England, Wales and the Netherlands.

The bacteria, which is an indicator of whether human or animal waste has entered the water supply, was detected at least once in 20 out of 929 public water supplies tested during compliance monitoring in 2010. This figure is down from 27 in 2009 and has fallen every year since 2004.

Public water supplies provide drinking water to almost three million people in Ireland.

Twelve per cent of private group water schemes were contaminated at least once during 2010. The number of private group water schemes where E.coli was detected fell from 87 in 2009 to 56 in 2010.

EPA deputy director general, Dara Lynott, said remedial works outlined by the EPA in 2008 will be complete in over 80 per cent of supplies by the end of 2011. "We will continue to target any water supplies that do not meet the highest standards. Ensuring that our drinking water is of the highest quality is vital for public health, for our food industry, for tourism, and for inward investment".

Almost 250,000 monitoring tests against national and EU standards are carried out to assess the safety of Irish drinking water annually.

Of the 339 supplies identified to be in need of remedial action in 2008, 49% (166) have been removed.

A further 67 new supplies were added to the remedial action list since 2008. By the end of 2011 just over 100 supplies will require the completion of outstanding remedial works to enable them to be removed from the list.

The report said the Vartry Reservoir which supplies parts of Dublin and North Wicklow, the Lee Road reservoir which supplies Cork City and Staleen which supplies East Meath and Drogheda will require significant investment to complete the remedial actions specified.

Dublin City Council warned yesterday that 150,000 homes in Dublin and Wicklow could be left without guaranteed drinking water for years if the Vartry tunnel collapses. The tunnel - which carries 80 million litres daily - represents about 20% of the total of the water supply to the greater Dublin area.