A consumer watchdog has warned that there is "no room for complacency" after 45,000 people in north Wales were told to boil their drinking water.
North Wales is no more prone to problems with drinking water quality than other areas, says Welsh Water.
The company said the current boil water notice for 45,000 customers around Bangor, Gwynedd and parts of Anglesey was purely a precautionary measure.
It added that lessons had been learned from an outbreak of cryptosporidium in Gwynedd and Anglesey three years ago.
Customers who have been told to boil their water could receive £25 in compensation for their inconvenience.
"The water industry throughout the UK learned from the outbreak of cryptosporidiosis in north Wales three years ago and water monitoring standards were revised," said a spokesman.
"We have carried out risk assessments at all Welsh reservoirs, and we now monitor our treatment works extremely closely so that we can act immediately if we see any indication of cryptosporidium.
"This is precautionary because we aim to avert an outbreak of cryptosporiodiosis in the community."
He added that a £150m programme to upgrade water treatment works in Wales is planned, and this should further reduce the risks of customers being asked to boil their drinking water in the future.
"There is no reason to think that north Wales is more vulnerable than any other area in Wales," he said.
Welsh Water issued its third warning in three years after a rise in bacteria was detected at a treatment plant.
Welsh Water issued its third warning in three years after a rise in bacteria was detected at a treatment plant.
The company says the warning for customers in Gwynedd and Anglesey will stay in place for at least two weeks.
The company said: "As we expect the boiling notice to be in place for over a week, we will pay all the customers affected £25 to cover the cost of inconvenience of having to boil their water.
Diane McCrea, chair of the Consumer Council for Water Wales, said clean and safety water must be the priority.
"People do not have to contact Welsh Water to receive the money, it will be sent to all customers in the affected area by post over the next few weeks."
AREAS ADVISED TO BOIL DRINKING WATER Bangor, Bangor side of Felinheli (marina), Beaumaris, Bethesda, Capel Curig, Cwm y Glo Gaerwen , Gallt y Foel, Gerlan, Llanddaniel, Llanddeiniolen, Llandegai Llandegfan, Llanfaes, Llanfairpwll, Llangoed, Menai Bridge, Mynydd LlandygaiPentir, Rachub, Rhiwlas, Sling, Talybont, Tan y Foel, TregarthSource: Welsh Water
AREAS ADVISED TO BOIL DRINKING WATER Bangor, Bangor side of Felinheli (marina), Beaumaris, Bethesda, Capel Curig, Cwm y Glo Gaerwen , Gallt y Foel, Gerlan, Llanddaniel, Llanddeiniolen, Llandegai Llandegfan, Llanfaes, Llanfairpwll, Llangoed, Menai Bridge, Mynydd LlandygaiPentir, Rachub, Rhiwlas, Sling, Talybont, Tan y Foel, TregarthSource: Welsh Water
Mrs McCrea said the council's job as consumer champion was to challenge the water company on customers' behalf to deliver "the safe quality drinking water that they expect and deserve".
Meanwhile, Diane McCrea, chair of the Consumer Council for Water Wales, said there was "no room for complacency" and that clean and safety water must be the priority.
She said: "I understand that the company is in the process of upgrading the treatment works which is involved in this outbreak.
She said: "I understand that the company is in the process of upgrading the treatment works which is involved in this outbreak.
"I will be calling for the company to get its other remedial works done as quickly as possible," she added.
"I will be calling for the company to get its other remedial works done as quickly as possible," she added.
Mrs McCrea said welcomed stringent new regulations water companies were now required to give consumers warnings as soon as there was any evidence of bacteria in water supplies.
Mrs McCrea welcomed stringent new regulations requiring water companies to give consumers warnings as soon as there was any evidence of bacteria in water supplies.
"It's no good waiting until people are ill. They have to be given the warning to boil their water and take precautions themselves."
"It's no good waiting until people are ill. They have to be given the warning to boil their water and take precautions themselves."
We have a grandmother living here... and she's very fragile, so I'm concerned as to how that would affect her Hannah Hughes, Llanfairpwll The advice to boil applies to the Bangor, Menai Bridge and Llanfairpwll areas, as well as the village of Capel Curig.
One resident, Hanna Huws, of Llanfairpwll, who has to boil water for the second time in three years, said: "We have a grandmother living here - my mother-in-law - and she's very fragile, so I'm concerned as to how that would affect her.
One resident, Hannah Hughes, of Llanfairpwll, who has to boil water for the second time in three years, said: "We have a grandmother living here - my mother-in-law - and she's very fragile, so I'm concerned as to how that would affect her.
"And also of course there's all the boiling of the water - there's seven of us living in the house."
"And also of course there's all the boiling of the water - there's seven of us living in the house."
We have a grandmother living here... and she's very fragile, so I'm concerned as to how that would affect her Hanna Huws, Llanfairpwll
The area's tap water comes from the Mynydd Llandegai water treatment works, which takes supplies from the Marchlyn Bach and Ffynnon Lligwy reservoirs.
The area's tap water comes from the Mynydd Llandegai water treatment works, which takes supplies from the Marchlyn Bach and Ffynnon Lligwy reservoirs.
Reservoir
Reservoir
Welsh Water has apologised for the inconvenience to customers.
It said an increase in levels of cryptosporidium was found after "routine water quality sampling," which "prompted us to take this precautionary measure to protect public health."
The company said "extensive" further water sampling was needed.
Cryptosporidium is a parasite found in humans and animals and can cause temporary diarrhoeal illness. Its eggs are killed by boiling water.
Cryptosporidium is a parasite found in humans and animals and can cause temporary diarrhoeal illness. Its eggs are killed by boiling water.
The National Public Health Service for Wales has asked local GPs to report any cases of diarrhoea and to take samples to be tested for gastrointestinal infections such as cryptosporidium.
The National Public Health Service for Wales has asked local GPs to report any cases of diarrhoea and to take samples to be tested for gastrointestinal infections such as cryptosporidium.
It is "closely monitoring" the levels of illness in the area affected and advising people to maintain good personal hygiene - including washing hands with soap and warm water if they had vomiting and diarrhoea or were looking after someone who was ill.
It is "closely monitoring" the levels of illness in the area affected and advising people to maintain good personal hygiene.
For several days in mid-August, almost 5,000 people in the Tywyn, Aberdyfi, Bryncrug, Rhyd-yr-Onen and Brynglas areas of Gwynedd were also advised to boil their tap water after the quality was affected by heavy rainfall.
For several days in mid-August, almost 5,000 people in the Tywyn, Aberdyfi, Bryncrug, Rhyd-yr-Onen and Brynglas areas of Gwynedd were also advised to boil their tap water after the quality was affected by heavy rainfall.
It followed tests which showed some cryptosporidium parasites in the water.
In November 2005 a total of 231 people were left ill in Gwynedd and Anglesey after cryptosporidium affected a Snowdonia reservoir.
In November 2005 a total of 231 people were left ill in Gwynedd and Anglesey after cryptosporidium affected affected a Snowdonia reservoir.
The water company was fined £50,000 after admitting supplying unfit water in that case.
The water company was fined £50,000 after admitting supplying unfit water in that case.
An investigation is under way by the Drinking Water Inspectorate into the latest case and Mrs McCrea said she would be urging it to make its report public as quickly as possible.
An investigation is under way by the Drinking Water Inspectorate into the latest case and Mrs McCrea said she would be urging it to make its report public as quickly as possible.
She will also ask the water company to distribute bottled water immediately to people on their vulnerable register.
She will also ask the water company to distribute bottled water immediately to people on their vulnerable register.
Any customers who want more information can call 0800 052 0130.
Any customers who want more information can call 0800 052 0130.
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