The number of people suffering from a stomach bug outbreak in north Wales continues to rise with 138 cases identified - up 15 on the previous day.
Health officials are continuing to investigate if sewage entering water supplies at Cwellyn reservoir caused the cryptosporidiosis bug outbreak.
About 70,000 households in Gwynedd and Anglesey have been told to boil their drinking water into the new year.
DNA tests are being carried out on the bug to discover its source.
A statement released by the outbreak control team - which includes the Environment Agency, councils, Welsh Water and public health bodies - said 15 new cases had emerged between Thursday and Friday.
Residents wishing to find out whether their home's supply is affected can check their postcode against a list held by Welsh Water at any time by ringing 0800 052 0130.
NHS Direct is operating two help lines on 0845 850 9850 and 0845 600 6086 between 0900 GMT and 1800 GMT on weekdays, and 0900 GMT and 1700 GMT at weekends.
The statement said: "All septic tanks near to Cwellyn reservoir have been checked for the possibility of sewerage leakage or water supply penetration.
"Daily monitoring of the water quality is continuing, with samples being taken at different points along the reservoir."
The bug is thought to have contaminated Cwellyn reservoir via untreated human sewage, despite water tests showing only low levels of cryptosporidiosis there.
Experts have so far been unable to pinpoint a definitive source of the bug and about 70,000 households have been urged to boil tap water before drinking it until at least 9 January.
The affected area includes Bangor, Caernarfon, Beaumaris and Menai Bridge.
Only low levels of the bug have been found at the reservoir
On Thursday, Welsh Water said customers might receive compensation for weeks of having to boil their drinking water, but the cause of the outbreak of cryptosporidiosis had to be established first.
A spokesman for Welsh Water said: "Although the Llyn Cwellyn reservoir is being investigated, at present we do not know for certain that it was the source of the problem."
Symptoms of the cryptosporidium bug are diarrhoea and stomach cramps and it typically lasts for around a fortnight.
Public health experts have said the outbreak should "burn itself out", but if that has not happened by early January, the advice to boil water will be extended.
Meanwhile, Cardiff law firm Russell Jones and Walker said on Friday that a teenager from the Caernarfon planned to sue Welsh Water after falling ill with the stomach bug.
Welsh Water said it was premature to talk of legal action while investigations to trace the source of the cryptosporidium outbreak were ongoing.