Outdoor plumbing

So, I have some outdoor water lines that are regular looking small diameter (I think 3/8") PVC. Not sure how long it has been in place (more than 6 years, and it didn't look new then), and a portion of it is exposed to direct sunlight. This system supplies water to a spigot up on my deck, a spigot in the back yard and then runs under my pier to a sink and another spigot. The system has a shutoff valve in the garage and has several drain valves so I can isolate and drain the system for winter.

I turned the water on the other day and the vertical run of PVC going up to the deck (exposed to direct sunlight) has several splits in it. I was going cut out and replace that section, but am thinking that the rest of the PVC that is not underground is probably similarly brittle and near failure. If I wanted to replace the above ground portions exposed to sunlight in their entirety, what is the correct material?

The portion feeding the deck spigot comes out of the ground and goes vertically maybe 15' feet then horizontally maybe 6', then vertically maybe 3' to the spigot. I could relocate the spigot up there to simplify the run if need be and get rid of the horizontal run.

The other above ground portion runs under my pier and that run is about 120' and this is not exposed to much direct sunlight since it runs under the decking.

The remainder of the system is underground. Maybe 10' from the house to where the deck line taps off and then another 20' to where the pier starts. I don't think I need to dig that part up.

Ideas? Thanks.

Unless there is some other better suited material, I am thinking about replacing the failed section with PVC and maybe painting it to provide some UV protection. Not having water out on my dock is hampering my ability to take the jet ski out because I need to flush the salt water out after using it and I have no water out there at present.

In reply to T.J. :

That, or just stick a piece of foam pipe insulation around it?

Our PVC water line sticks up out of the ground about a foot before it comes into the house. We do typically see freezing temps here in winter(thankfully for short periods), so I have some insulation around it. Granted, it doesn’t get much direct sun, and pretty much only in the cooler months, but it seems to have held up ok so far. 

Black plastic HDPE water pipe is UV resistant and designed for exactly what you're doing.

If the existing pvc has held up for a decade, I bet painted pvc would hold up for even longer. No sense over complicating it. 

So, it turned out the existing system was 1/2” cpvc and I’m pretty sure it failed not from chronic UV exposure, but due to operator error. When I drained the system last fall, I opened the spigot, but did not bother disconnecting the hose and it has a nozzle on the end that apparently seals well. As a result, I surmise I had water trapped in the vertical section of pipe that failed, that subsequently froze and split it. 

Anyway, I replaced the broken pipe with new and all is good now.