It may be, hard to say for sure. PVC pipe is not supposed to be used inside, but sometimes a DIYer will contrive something illegally with it. You should know that if you install a sprinkler system using domestic water, you must use a backflow prevention device to avoid the possibility of contaminatimg your household water. If you are using a hose attached to a hose bib coming from the house water, the bib needs to be the anti-syphon type. Regulation enforcement on this varies from place to place, so you should check with your city as to their requirements. For example, my city requires an annual inspection by a licensed technician, but other areas seem to ignore the issue.