Scottish Water engineers are still trying to fix the burst main in St Vincent Street, which burst almost a week ago.
But traders have hit out at water bosses for failing to repair the main for five days.
Early today supplies were cut off to customers in the Trongate area while staff worked to fix the leak.
Scottish Water had said the fault was difficult to repair because of the pressure on the main.
A spokesman said today: "Engineers are continuing to work on a complicated repair.
"Working through the night, our staff have restored water to customers who were without supply as repairs continued. Water leaking from the main has also been significantly reduced."
Streets in the city centre were flooded yesterday as water gushed out on to a stretch of St Vincent Street, spilling out on to West Nile Street and Renfield Street.
As reported in later editions of yesterday's Evening Times, Scottish Water is working in the area as part of an upgrade to the network of pipes.
But business owners fear the leak and works are costing them customers. Several bars, shops and restaurants in West Nile Street have been affected by the burst pipe.
Craig Thomson, boss of clothing shop Fat Buddha Store, in West Nile Street, said: "I noticed it on Friday and called Scottish Water. I was told someone would come out.
"We're worried the water could come into the shop.
"I have seen tourists taking photos of the water gushing out and there are fewer people walking past our shop because there is water everywhere."
Part of St Vincent Street, between its junction with West Nile Street and Renfield Street, has been closed for parking while the work continues.
Linda Brown, of Fired Earth Interiors in St Vincent Street, said: "It is a real worry for us.
"Scottish Water closed the other side of the road while they do the works but that is where our customers normally park so they can carry heavy tiles or furniture a short distance to their cars.
"People are being put off from walking near the shop as we're almost surrounded by water."
Pam Hunt, 57, of Shawlands, works at a solicitors' office in St Vincent Street. She said: "My colleagues and I are disgusted about the massive amount of water gushing down St Vincent Street and Renfield Street.
""The water outside the Drum & Monkey pub was bubbling up about a foot.
"People are having to walk into the road. I have seen at least two people almost hit by traffic."