Syrian forces have reportedly entered the village of Ain al-Fija near Damascus, which controls the capital's water supply.
More than 5 million people in Damascus have been without running water since late December after armed opposition groups allegedly contaminated water plants with diesel.
Troops from President Bashar al-Assad's Syrian Arab Army are said to have taken control from the armed groups on Saturday (28 January), a Hezbollah-controlled media outlet reported.
"The Syrian army has entered Ain al-Fija… and raised the Syrian flag over the spring installation," it said in a statement, reported Reuters.
The Wadi Barada valley, where Ain al-Fija lies, has been subjected to an intense bombing campaign by Russian-backed Syrian forces despite the ceasefire agreed in December.
However, militants in Wadi Barada – including the al-Qaeda-linked Jabhat Fateh al-Sham and the Turkey-backed Ahrar al-Sham – were outside of any ceasefire agreements, allowing Syrian forces to continue their advances.
The militants were the centre of a row at the recent Astana peace talks in Kazakhstan, when opposition negotiators allegedly defended the militants' actions, in spite of their agreed illegality.
But the two-day conference, which took place over 23- 24 January, ended in "good progress" according to Syria's top negotiator Bashar Jaafari who promised further advances.
State-run media SANA confirmed on Saturday that a deal had been reached between militant groups and the Syrian government.
Ali Ahmed Yousef told the outlet that militants agreed to leave Ain al-Fija and were headed to Deir Maqrin village, in Idlib province.
The development is a positive sign before further peace talks are held in Geneva, which will be overseen by the United Nations.
The talks were due to take place on February 8. However, Russia's Foreign Minister Sergey Lavrov on Friday stated the talks will be postponed to the end of the month. The UN has yet to confirm the delay.