Per Oren:
My house is PEX and I trust it. There are various types of PEX, even
for natural gas, etc. It is now being used in landscape irrigation,
too. There is a Thermal-PEX also that has a foam tube surrounding it
for hot & cold lines for out buildings.

The state parks around here use some sort of white plastic for their
water pipes. Dunno if it's "PEX", but it makes the water taste quite
bad - borderline undrinkable.
--
Pete Cresswell