New ultra violet equipment has been installed at the Mynydd Llandygai plant
Thousands of people in north Wales have been told they no longer need to boil their tap water as it is now free from a bug and safe to drink.
Welsh Water Dwr Cymru customers around Bangor and parts of Anglesey were issued with the advice in August.
But their water supply has been treated and is free from the cryptosporidium bug which can cause stomach upsets.
New equipment at the Mynydd Llandygai treatment works near Bangor has been installed to kill the parasite.
A link between a number of stomach upsets across the region and the cryptosporidium-infected water was ruled out by the National Public Health Service on Wednesday.
In north Wales we have tended to rely on the fact that the water in the upland reservoirs is really quite clean and quite pristine - however, in the last couple of years we have seen things change
Tim Masters, Welsh Water
Cryptosporidium was found in the water at the plant when routine sampling revealed an increase in its levels.
A boil water notice was subsequently put in place for about 45,000 Welsh Water customers in the Bangor, Bethesda, Capel Curig, Llanfair PG and Menai Bridge areas as a precautionary measure on 29 August.
Ten cases of crytosporidioisis in the area have since emerged, but public health officials have said none can be linked to problems with the water.
A new ultra violet water treatment process has been installed at the plant serving most of these areas which will kill any cryptosporidium present.
However, the village of Capel Curig will continue to receive its water from another source until the same process can be installed at the small treatment works which serves that specific area.
Welsh Water operations director Peter Perry said: "We are pleased that we can now lift the boil notice and end this inconvenience to local people.
"So far, there have been no reported cases of illness as a result of the cryptosporidium in the water supply.
"I would like to thank people for bearing with us while this precautionary boil water notice was in place."
Asked why the area seemed to be more vulnerable, Welsh Water's Tim Masters said: "In north Wales we have tended to rely on the fact that the water in the upland reservoirs is really quite clean and quite pristine however, in the last couple of years we have seen things change.
"We have had a couple of wet summers and whether this is a forerunner to future climate change issues - we have seen a change in the water quality we have been treating and that's why we have had to do this."
He was asked whether the water quality is being affected by run-off from the land.
"It could well be, we have had two very wet summers, very different from what we have previously experienced," he added.
The company will send customers a £25 cheque within 21 days as compensation for the inconvenience caused.
Welsh Water also announced it is speeding up a further £9m investment at the plant to further improve its overall water quality.
It is the third time in three years that the company has issued warnings over the supply in north Wales.
In November 2005, 231 people were left ill in Gwynedd and Anglesey after cryptosporidium affected a Snowdonia reservoir.
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