writes:

So, what about that PEX pipe? How does that hold up in sunlight?

Normal PEX is not UV resistant.
There exists specialty PEX that, apparently, is
http://www.seymour-ind.ca/displayProduct48.php
Why not just use an old garden hose ?
John T.

Why not use a garden hose???

Well, the last hose I bought had a warning on it not to drink
from it. It said the hose leaches toxic agents into
the water.

Normally I discount these kinds of warnings as some company
trying to avoid a lawsuit but Google seems to confirm.

Perhaps real underground water pipe is the best answer.

--
Dan Espen