The measuring tube of the in-line measuring device is formed by means of a support tube and a liner internally lining the support tube. The liner adheres to the support tube, with interposition of a mediating primer. Both the primer and the liner are composed, at least in part, of polyurethane. Especially, both the polyurethane of the liner and also the polyurethane of the primer are suitable for drinking water applications, so that the in-line measuring device itself is also suited for measuring drinking water.