FYI the "new" here is this specific trial, not the use of water/sewer pipes for fibre, which has been happening for about 15 years now.

i3 is an infrastructure company that do this. They trialled a sewer-based fibre network in Bournemouth where I grew up back in ~2010, although it never quite got past the trial stage due to contract issues. They've done similar trials in South Africa, Australia, US, and elsewhere. Not sure if any have rolled out to full scale usage but it's been long enough that I'd expect some have.