The message
from "Dave Plowman (News)" contains these words:

You aint seen the Electron Scan Photographs I have seen!
Could you accept that cheap extruded EDPM (synthetic rubber), made down
to a price and not made to any standard, can have a rough inner
surface. Could you accept that dearer EDPM hose, made to quality
standards, can be made with a smooth inner surface and tested as such
and against harbouring biofilms by an independant laboratory?

Have you seen just how 'rough' the average pipe is in a hard water area
after a short time in use?

And anyway - smoothness doesn't ensure biofilms don't form - try
sticking a mirror in some water for a few days.

--
Skipweasel
Pay no attention to the man behind the curtain.