Security will be stepped up for the global climate summit in Paris, with civil and military forces deployed to guard the venue where 140 world leaders and up to 40,000 delegates are due to meet next week.
French authorities have insisted the summit, known as COP21, will go ahead despite the terrorist attacks that killed 130 and left hundreds injured in Paris earlier this month.
Prime minister Manuel Valls said the event, due to begin next Monday, would be held because "it's an essential meeting for humanity" and would be an opportunity for world leaders to show their solidarity with France.
In order to protect the water system from attack during the conference, sensors have been installed in the network to monitor pressure, chlorine levels, temperature and conductivity – parameters that could signal whether there is any contamination of the water supply.
"A terrorist could very well take advantage of this gathering to strike," Jean-Louis Fiamenghi, head of security for French water and waste company Veolia, told Reuters. He added that there had been no threat of nuclear, biological or chemical threat at any Veolia sites across France, however.
Conference participants will be in a closed, protected area at the venue at Le Bourget, north of Paris, as they work towards a deal to limit rising greenhouse gas emissions.
Security within that inner zone will be the responsibility chiefly of the United Nations, but French authorities will guard the buildings and control access to the complex.
Some public demonstrations planned to coincide with the talks have been cancelled under a state-of-emergency decree that remains in force until February.
The French government said 140 heads of state and government were due to attend the opening day of the summit on Monday. They include US president Barack Obama, who said he would go ahead with the visit despite the attacks and urged other leaders to do the same as a way of showing defiance in the face of terrorism.
“I think it’s absolutely vital for every country, every leader, to send a signal that the viciousness of a handful of killers does not stop the world from doing vital business,” Mr Obama said.
Among the events cancelled by the government are large demonstrations that were due to take place in Paris and other French cities on Sunday, the eve of the summit.
A number of events scheduled for December 12th, the day after the conference closes, have also been called off.
Authorities initially looked at relocating the Sunday march, which was to take place between Rue de la République and Place de la Nation, but that was ruled out. The foreign ministry said only indoor events could go ahead under the tight security restrictions.
"The security of everything within the rooms of the conference we will guarantee 100 per cent, because it will be under our control, but we can't completely ensure the safety of the external part," French foreign minister Laurent Fabius said.
Climate 21, a coalition of NGOs and trade unions, said it regretted the decision but was “more determined than ever” to make its voice heard on climate justice. It would find “creative” ways to have its say, the group added.
Access to Le Bourget will be strictly controlled. People entering the conference area will pass through security scanners, and vehicles will be screened for bombs.
Some 30,000 police will be on duty around Le Bourget and at French border checkpoints.