In article , "gribblechips"
says...
In an earlier contribution to this discussion,
JJJ wrote:

I've just bought a water filter cartridge unit, which comes with the
type of self-cutting connection you normally install on the copper
cold water pipe to the tap.

The water pipes here, however, are all plastic. Will this still work
or is it just designed for copper?

snip

I`d be a bit dubious too. That said, it would be about 10 mins work to let
in a short length of copper pipe on a couple of push fits.

It might be a bit neater to fit a tee.