There is no dispute that the Greater Dublin Area is facing the possibility of acute water shortages. New water-treatment plants at Ballymore Eustace and Leixlip will increase supply, but only up to 2016.
Dublin City Council calculates that the population of the Greater Dublin Area will be 2.4 million by 2031, a million more than at present. It will need 330 million litres of extra water a day.
In order to meet future water demand, a new major source will have to found.
The council has ruled out the rivers Slaney and Barrow as an option because the volume of water would not be nearly enough. This leaves desalination and extraction from Lough Ree on the Shannon as the preferred options.
Although the initial costs of both options are similar - between €550 million and €600 million - the process of converting salt water into drinking water is energy intensive and would cost €450 million to run over 20 years as opposed to €131 million for the Shannon option.
The Shannon Protection Alliance (SPA) claims the Shannon option is a done deal, pointing to a paragraph in the council's draft feasibility study which states that "Lough Ree option was identified. . .as the new major water source for the Greater Dublin Area".
However, Tom Leahy, deputy city engineer, denies this and says the council is conducting advanced hydrological surveys to address the concerns of local people.
He also said the council engineers were re-examining the North Leinster aquifer option, though initial reports have suggested it would only provide a fraction of the water needed.
"We have quite a wide range of studies into the very real questions we will have to address. We wouldn't be spending this amount of time and effort on these studies if decisions had already been made. They most certainly have not been made.
"People are reacting to what are misleading statements, as opposed to being aware of what the facts of the situation actually are. Some of that concern has undoubtedly been caused by public statements that the river Shannon is going to be as dry as the Dead Sea because of this proposal. That is, quite frankly, a gross and misleading exaggeration of the facts."
Mr Leahy says that while the council would propose an option, it would be Bord Pleanála whowould have the final say, and the respective merits of whatever proposal is chosen are likely to go through a long consultation period before getting permission.
The extent of the challenge facing the city is contained in a study by Dr Conor Murphy of NUI Maynooth, who has been studying the possible impact of global warming on Dublin's drinking supply.
He has forecast that available drinking water will decrease by 20 per cent by 2020 and by half by the middle of this century unless a major source is found.He has also forecast that water flow in the Rye Water, the main tributary of the Liffey where Dublin currently draws most of its water, will be reduced by half in summer because of the drier climate.
Greater Dublin area (GDA)
Population 2007:1.4 million
Population 2031:2.4 million (projected)
Expected water demand in Greater Dublin area
2007:550 million litres a day
2031:880 million litres a day
Level of water leakage in GDA
1997:40 per cent
2007:30 per cent
2031:20 per cent
Length of projected pipe from Lough Ree to Dublin:105 km
Proposed maximum abstraction levels
4 per cent of average flows of River Shannon into Athlone;
2 per cent at Lough Derg
