The linked article (and government push to do this) completely ignores the fact that this is done frequently now.

It's used to get the last few metres into the home, e.g. from the boundary to the inside of the house. You put a swept tee in at each end, after the stopcock. Water off, dig down adjacent to stopcock, cut pipe, shove a drinking water rated duct down the pipe through the small port on a swept tee. Shove some chlorine tablets in the pipe and couple up to the new swept tee. Repeat interception at other end outside or indoors, and then use standard fibre cable blowing through the inner microduct, and away you go.

There's a huge amount of disused water pipes in most developed nations which are frequently used, similarly using sub-ducting, and you can run cable through mains - but have to come out every time there's a valve, so practically it's usually cheaper to dig. Where it comes in handy is where there's areas you can't practically dig up, e.g. major roads with old pipes underneath.

Source: Have done a bunch of this for a major UK telco.

https://www.craley.com/craley-in-pipe-fibre

> I remember a while back that there has at least been cursory investigation into running high-speed internet cables through water pipes.

Oblig:

https://archive.google.com/tisp/index.html

https://archive.google.com/tisp/install.html

There is company in Czechia which provides optics via sewage. I guess it is cheaper to use existing infrastructure than to place new pipes under roads.

Sounds a bit like this "How TiSP Works" https://archive.google.com/tisp/install.html

"cheaper" is an understatement.