Massive queues of traffic formed through main routes in the city centre, including around George Square, during rush hour.
St Vincent Street was shut between West Nile Street and Renfield Street, while West Nile Street was closed southbound from West George Street to St Vincent Street.
The closures are expected to last until 6am tomorrow.
Scottish Water engineers began working at 7am yesterday and street diversions were in place through Bath Street and Renfield Street and through George Square.
As the work continued today it resulted in tailbacks to the Cochrane Street junction of George Square from about 7am.
The works are part of Scottish Water's £3.5million upgrade of the network of pipes in the city centre.
The company had stopped the work over the festive season to limit disruption to shoppers, businesses and road users.
Patricia Melly, the firm's project manager, said: "So far, we have renewed about 2½miles of pipes. We have completed our work in Sauchiehall Street and Renfield Street and reinstated the areas where we were working to the condition they had been in before we started.
"This included carefully restoring granite paving stones in Sauchiehall Street.
"Some disruption and inconvenience is inevitable with this sort of work in these city centre locations and we thank road users, pedestrians, customers and businesses for their patience and co-operation."