Millions of people have been without water for weeks after fighting damaged key infrastructure in the Wadi Barada region outside Damascus that is the main water source for the capital.
The Jabhat Fatah al-Sham terrorist group, formerly known as al-Nusra front, is present in Wadi Barada, and has cut water to Damascus since Dec. 22.
"The role of the Syrian Army is to liberate that area in order to prevent those terrorists from using that water in order to suffocate the capital," Assad told French media in an interview aired Monday, AFP reported.
He said "more than five million civilians have been deprived of water for the last three weeks".
The United Nations says 5.5 million people in and around Damascus are without water.
Assad said that Fatah al-Sham is "occupying" the Wadi Barada region, 15 kilometers (10 miles) northwest of the capital and that his forces will drive them out the area.
Assad stressed that a recent nationwide ceasefire brokered by Russia and Turkey on Dec. 30 does not include Fatah al-Sham and Daesh (ISIL or ISIS).
Meanwhile, Assad rejected any negotiations towards his departure from power at talks set to be held in late January in Kazakhstan's capital Astana.
"My position is related to the constitution, and the constitution is very clear about the mechanism in which you can bring a president or get rid of a president," he said.
"So, if they (the opposition) want to discuss this point, they have to discuss the constitution, and the constitution is not owned by the government or the president or by the opposition.
"It should be owned by the Syrian people, so you need a referendum," he said.
The Astana talks, organized by government allies Russia and Iran and Turkey, aim to pave the way towards an end to a nearly six-year war that has killed 310,000 people and displaced millions.