IRISH Water has told 126 households in Bishopswater that their water isn't fit to drink without the tap being run for between five and 10 minutes to flush out lead contamination.
It says it has sought advice from the HSE which says household water can be used for toilet flushing, bathing. showering, laundry and dishwashing.
But only water from the rising main which feeds the cold tap in the kitchen can be used for cooking and drinking and then only after the tap has been run for a minimum of five minutes.
Irish Water has told residents that the problem was uncovered after the utility took water samples at addresses throughout Bishopswater.
'The test results confirm that there were exceedances of the maximum allowable concentration for lead in the random daytime and stagnation samples,' it says in the letters sent to the householders.
Irish Water says the lead in the water is most likely to have arisen from the service pipe from the distribution watermain and/or internal plumbing at the address, or addresses, were the water sample was taken and not from the treatment plant or distribution water mains.
It says that while it intends to invest in the public side of lead pipe replacement and will target areas initially in those thought to be at the greatest risk, the replacement of private lead service pipes 'is the responsibility of the property owner'.
'After having your premises assessed for the presence of lead pipes, you should consider having it replaced.'
The maximum concentrations of lead allowable in drinking water is 10 parts per billion. Some of the samples taken in Bishopswater, the results of which have been seen by this newspaper, ranged from 10.3 to 11.
Irish Water says that once residents have replaced their 'private lead service pipe and internal lead plumbing' you should contact them 'to replace the remaining public side lead service pipe'.
'If you have any health-related questions, HSE advice is to contact your GP.'
An HSE consumer notice, accompanying the Irish Water letters gives the following advice:
* Lead can affect the development of a child's brain leading to problems with learning, behaviour and attention.
* The risk is greatest for young children, infants and babies in the womb.
* Lead may harm the kidneys and may contribute to high blood pressure. It has also been linked to cancer.
* These health problems were discovered at very high levels of lead. We now know that even low levels can have health effects.
* No level of lead in drinking water is now considered to be completely safe.
* It is therefore best to keep everybody's exposure to lead, from all sources (drinking, eating, inhaling), as low as possible.
* Everybody should therefore try to drink water with as little lead in it as possible.
It says water supplies that come under the European Union (Drinking Water) Regulations are tested for lead.
'Houses and buildings served by these supplies are randomly chosen for testing. Your individual property may not have been tested previously.
The water testing results of your water supply are available for you to see. Contact your Local Authority for public water supplies (operated by the LA on behalf of Irish Water) and also for all private regulated supplies including group water schemes. The Environmental Protection Agency (EPA) publishes a yearly report with a summary of drinking water results from all Irish regulated drinking water supplies.
Outside the tests, local people are being told that if their homes were built before the mid-1970s they may have lead pipes or the lead pipes may have been replaced, but 'after the mid-1970s it is unlikely to have lead pipes'.
'If you suspect you may have lead pipes, look for them.'