Leaking pipe from communal tank or condensation?

[Benny_the_ball-valve]

A friend has had a leak in the bathroom of his leasehold local authority flat. This was due to a tap connector on the basin that had worked loose. I have now fixed this but in the process took a look under the bath to check out the future fitting of a replacement bath/shower mixer. The cold water supply pipe (1" steel) appeared very wet indeed. This pipe tees off from a vertical pipe that is (flush fitted inside the wall) which is connected to a tank on the roof. This pipe similarly supplies the two flats above and one below. I can just about get my hand up a few inches of the vertical section of the pipe and it feels very wet here also, though it appears to be pretty well insulated.

If there is a leak it is outside my mate’s responsibility and he will need to get the LA to have it inspected and repaired. Is it possible, though, that this could be condensation? If so, what can be done to prevent it, as this would be likely to cause damp in future?

Thanks for any help.