Yes, because the non licensed people can cause a cross connection with the potable water system
not for your own property.
Not necessarily, depends what and where plumbing work is to be done. Check with local plumbing authority about needing license or not. Sometimes you need license to pull permits to do plumbing work. Plumbers usually have at least a journeyman's license.
I think you just need insurance or get a contractors license http://www.rld.state.nm.us/CID/faq.htm
license for plumbing what it looks like
New York State does not license "handymen." The state may require a business license if you are conducting a business, and you may need a plumbing license or electrician's license if you will do plumbing or electrical work.
The only plumbing work that you are allowed to perform without a license is for your own property.
Each State in USA have their own standards for plumbing jobs. Most States need the plumbers to hold general license, master license or contractor's license pertaining to that State.
Drop out of High School.
Having a license to install siding is not mandatory. You can install siding on your home with no license. However, if you are hiring a professional to install the siding for you, although having a Contractor's License is not required it is recommended.
You will need to go to school to obtain a plumber's license. Vatterott is one national university that can help you earn your license.
Only if you don't get caught
The plumbing and sanitary codes and violations of them, are not established as felony offenses.