Eddie,
PEX was used in the late 70's and early 80's in Southern California.
Unfortunately, there was a serious problem with it and the builders and
Shell Chemical (which made the PEX plumbing components) were sued - and
lost, big time. The PEX water lines had to be replaced with copper.
The problem, then, was that the fittings did not stay connected under the
continuous pressure of the city water supply. The PEX tubing exhibited "cold
flow" and slowly (until the end) slipped off the fittings causing major
water damage.
I do not know how well this problem has been solved - either by
reformulating the tubing, or redesigning the fittings and the attachment
scheme, or both.
If I remember correctly, the PEX plastic was potentially an excellent
material for potable water lines, as it was chemically inert to the water
and trace chemicals, and did not leech toxic chemicals into the water
passing through it.
Oliver Filippi