Hello I'm Mike and new to this site. I am going to replace some plastic plumbing under a double vanity.The drain lines are pvc and the water lines are cpvc. Is there a reason for this ?Can you glue cpvc to pvc ?

Cost. PVC for drains are allowed. PVC is typically allowed for cold water supply. CPVC must be used for hot water supply.

Both use different cleaner/primer and cement. Some codes dictate which cement and primer you can use.

PVC and CPVC cannot be glued directly together, but you could use femal and male adapters for the appropriate pipe.

KISS is correct but you can use purple primer on both but they need different cement. Oatey makes both a clear primer and purple primer that work on PVC and CPVC. Our building code does not allow clear because the inspector can't see that its been used, the purple stands out.