BBC Wales news website
Public health officials have advised 70,000 households in north Wales to boil or buy their drinking water until 9 January.
Over 12m bottles of water could be used during the outbreak
The warning was issued to protect against the parasite Cryptosporidium, which can cause unpleasant stomach problems. The outbreak has been linked to a Gwynedd reservoir.
The advice is an essential health precaution, but what are the environmental consequences of so many people boiling or buying bottled water for the next few weeks? The BBC Wales news website investigates.
In the last couple of years the term "carbon footprint" has become one of the more fashionable terms used by environmental campaigners.
It's the idea that people can judge their impact on the environment by measuring the amount of carbon dioxide their lifestyle gives off.
If you fly frequently or drive to work every day - both activities burning a lot of fossil fuels - the chances are your carbon footprint will be much larger.
Boiling all drinking water will also increase your "footprint" because of the extra energy consumption.
And buying bottled water has an even bigger impact when the production of the plastic bottles and all those trips to the shops are taken into account.
But how much exactly?
Energy expert Steve Smith estimates that an extra 80 tonnes of C02 a day could end up in the atmosphere if all 70,000 households bought their drinking water.
That adds up to 3,365 tonnes of C02 and almost 8,500 MWh of energy (a household typically uses 31 MWh a year) while the control measures are in place.
Mr Smith, from renewable energy specialists Dulas, said it would be better to boil the water from an environmental point of view - although that would still produce an extra 31 tonnes a day of C02.
The average carbon footprint for someone in the UK is currently 9.5 tonnes a year, according to International Energy Agency figures.
Mr Smith told the BBC News website: "That's a significant amount of carbon dioxide to be adding into current emissions, considering we are all trying to reduce it at the moment.
"There are some assumptions in these figures and they are based on a worst case scenario - but the environmental impact of these measure is still a very real concern."
Researchers at the Machynlleth-based Centre for Alternative Technology say the "target footprint" should be nearer two tonnes per year, based on calculations of how much C02 the earth can absorb.
But as well as the carbon dioxide emissions, Mr Smith has calculated that local authorities affected could have to dispose of 17.5 tonnes of plastic bottles a day - a total of 12 million bottles between now and 9 January, when officials hope to relax controls.
Figures assume 10 litres per day per household
Extra energy if boiling water: 73,427 kWh per day
Extra C02 if boiling water: 31.57 tonnes per day
Extra energy if buying bottled water: 204,887 kWh per day
Extra C02 if buying bottled water: 82.08 tonnes per day
Source: Dulas renewable energy specialists
Both councils - Gwynedd and Anglesey - told the BBC they would recycle all the extra bottles produced while control measures were in place.
A spokesperson for Gwynedd Council said: "Gwynedd Council has already installed special skips for plastic bottles located at the Council's municipal waste sites at Ffridd Rasus, near Harlech and Rhyngddwyryd, near Garndolbenmaen."
Anglesey Council said: "All but one of the small number of affected areas on Anglesey fall within the County Council's weekly kerbisde collection scheme.
"The kerbside vehicles collecting plastic bottles to be recycled by the public will have enough capacity to cope with the increase."