The two tunnels, each 48in in diameter, date from 1886 and 1924. Traditionally, they carried treated drinking water from the production plant at Invercannie, just west of Banchory, into Aberdeen. The £8m upgrade involves a complete refurbishment of the 1924 aqueduct, while the tunnel from 1886 will instead carry raw water from the River Dee to the production plant at Mannofield, in the city, where it will be filtered and made fit for drinking.

Together the aqueducts carry an average of 49 million litres of water a day.

Dave Milne, project manager for Scottish Water Solutions, said: "The work due to get underway in Banchory next week is to investigate the cross-connection, a major pipe and set of valves which link the two aqueducts.

"The aim is to seal off this connection, as we don't want raw river water mixing with the treated drinking water going to customers' taps. Our contractors will do their best to keep disruption to a minimum. The end result will be a more efficient use of Aberdeenshire's water infrastructure."

To enable the work to be carried out safely, three-way traffic lights will operate at the junction of Station Road and Raemoir Road, in Banchory. The company thanked motorists for their patience in advance and assured them that every effort would be made to keep traffic flowing as normally as possible.

The work, to be carried out by Carillion Utility Services, is scheduled to last up to three weeks but the traffic lights could be removed sooner, depending on progress. In planning the work, advice was taken from Aberdeenshire Council's roads department.

The £8m aqueducts upgrade is part of Scottish Water's 2010 Vision for Aberdeenshire - a £62m campaign of improvements across the region.