Towards the end of the nineteenth century, urban development and changing domestic habits substantially increased the demand for water in Edinburgh and other conurbations.

The private railway would run southwards for about eight miles (13 km) along the valley of the River Tweed from east of Broughton station.

The Caledonian agreed to lay a second track, at the expense of the Water Trust, alongside its own single line from Broughton station to the point of divergence of the new railway.

At first a northwards branch line at Broughton was planned to extract clay for sealing the reservoir, but this was later changed, and the material was imported from elsewhere.

[2][page needed] The contract for the construction of the reservoir was let in April, and the substantial wrought iron truss bridge over the Tweed was completed on 20 August 1897.

The train was named "The Tweedsmuir Express" and consisted of six six-wheel coaches, modern bogie stock being unable to negotiate the line because of curvature and clearance issues.

Young was unable to respond to the situation, and the Water Trust now asked the Caledonian to work the private railway, but this was refused.

[2][page needed] Sir Walter Thorburn added a plea to continue the operation of the line to run public passenger trains for the benefit of the residents of Tweedsmuir.

[3][page needed] In subsequent years several approaches were made, but the Caledonian had evaluated the potential loss from agreeing to operate a branch line to such a small community, and continued to decline to do so.