Plumbers tend to not use PEX for plumbing because rodents can chew through and damage the pipes and cause water leaks.
However some plumbers do use PEX for plumbing if you want them too and some do prefer to use it as it's pretty easy to connect and you don't have to glue or solder pipe joints together and PEX can easily be bent and snaked through walls easily.
CPVC pipe is good for hot water as CPVC pipe can handle hot water temperatures up to 200 F and it can also be used for cold water as well.
CPVC pipe can be used for supplying both cold and hot water in plumbing systems as CPVC is made to hold up to both hot water and cold water and PVC is meant to only handle cold water but PVC can handle water temperatures up to 140 F.
You can also use PEX or Copper piping for hot and cold supply lines in plumbing systems.
You can use schedule 40 PVC pipe for drinking water but it should not be used for hot water as it could melt but for cold water PVC pipe is okay and okay for drinking water.
You should not use PVC pipe on water lines that exceed water temperatures above 140 F as it can become toxic and could melt and leak.
PVC has a melting point of 180 F and the higher the temperature the faster it begins to melt.
The melting point on some grades and types of PVC can be as high as 500 F but most PVC begins to melt at 180 F.
PVC pipe does become toxic when heated as it has been found that when heated the PVC releases toxic hydrogen chloride gas.
PVC pipe can be used on hot water lines as long as the hot water does not reach higher than 140 F.
The primer on PVC pipes cleans the pipes and makes it easier for the PVC pipes to bond together as it also softens the plastic of the PVC pipes.
Plumbers use purple primer on PVC as it cleans the pipes and fittings of dirt, oil, grease or other foreign matter that can make it difficult for the PVC cement to bond the fitting and pipe together.
The Purple primer when used on PVC pipe also softens the plastic of the pipe so that it bonds together easier as well.
Before turning on the water you should allow the PVC glue to dry and cure for at least 2 hours.
It takes at least 15 minutes for the PVC glue to get a good bond with the pipe and fittings but for full strength it takes up to 2 hours.
So you should always wait until 2 hours have passed before you pressurize the water system and turn the water on because turning the water on too soon could cause the pipes and fittings to come apart.
The PVC glue melts the pipe and fittings together through a chemical reaction.
It does not glue the pipe like normal glue but instead melts the pipes together to form the bond and it can take 2 hours for the reaction to fully work and create a good permanent strong bond.
Also when putting the pipe and fittings together make sure to twist the pipes and fittings back and forth and hold them together for about a minute.
Holding the pipe and fittings together helps keep the pipes and fittings from pushing apart.