I remember a day when plumbers were changing cold water pipes in our apartment building in Russia. They were called in because the water was barely sipping from taps and it lasted for pretty long while and when it almost stopped running at all they were called in. When they cut off the old pipes they showed us what was inside and it still stays in my memory. The pipe was fully stuffed by some totally unpleasant looking something with a thin thin small hole in the middle. Looks like in the past few years nothing much changed as here are some pipe samples posted by various Russian plumbers across variety of Russian websites which were compiled in this post.
The cavity inside the pipe is getting smaller and smaller overgrown with dirt.