Can anyone tell me why PVC should not be used as hot & cold water distribution piping?
Thanks.
It does not hold up to the constant pressure and heat of a distribution system. If you want to use a similar product, use CPVC that is approved for this application.
Cuz the codes say so. . . 
This may help explain a little.
http://www.harvel.com/tech-specs-pvc-pipe-40.asp
Corrosion resistant pressure pipe, IPS sizes 1/8” through 24”, for use at temperatures up to and including 140 °F.
Also refer to IRC:
P2904.5
Hope this helps.
Marcel 
