Foreign Minister Shimon Peres told parliament that Israel did not and would not "tolerate unilateral measures".
His speech came just before Lebanon inaugurated a new pumping station on a river a mile (1.6 km) from the border - a move the Israeli Government has said could provoke war.
The installation will draw water for irrigation and drinking from a tributary of a river that feeds the Jordan River and Sea of Galilee - Israel's largest freshwater reservoir.
The high-profile ceremony was attended by Lebanese President Emile Lahoud and cabinet ministers along with representatives of the European Union and Russia.
Also present were hundreds of villagers who clapped at the defiant speeches by Lebanese politicians as the station started pumping water from the Wazzani River.
"This is not the end, this is just the beginning", said Lebanon's Parliament Speaker Nabih Berri.
Despite American efforts to dissuade the Lebanese, the Beirut government said it would not go back on its plans - a stand backed by the militant group Hezbollah.
The BBC's Kim Ghattas in Lebanon says people in area are grateful for the project - one of the first substantial contributions to the development of the south since the Israelis withdrew more than two years ago.
'Grounds for war'
As final preparations were made on Tuesday, Israeli warplanes circled the area.
The Lebanese Government argues that it is within its rights to use the new station, which it says will add an extra four million cubic metres (140 million cubic feet) a year to the seven million cubic metres it currently draws from the Hasbani River.
Hezbollah - which has routinely skirmished with Israeli forces since their withdrawal from southern Lebanon in May 2000 - has pledged immediate retaliation for any Israeli attack.
"The response will be very quick and I am not exaggerating if I say within minutes," said Hezbollah leader Sheikh Hassan Nasrallah on Tuesday.
Last month, Israeli Prime Minister Ariel Sharon was quoted by Israeli media as saying that the water issue constituted a "casus belli", or grounds for war.
The BBC's Kim Ghattas says the US and the EU have given assurances to Beirut that Israel will not launch any assault against the installation and destroy the new pump.
Envoys are still trying to mediate to ease the tension.
One idea has been for Lebanon to restrict its water usage to the needs of its local villagers as opposed to irrigation.
In 1964 Israel shelled Syria after it moved to divert water from the Banias River - a conflict which grew into all-out war in 1967.