This article explains how to mirror a website for backup purposes.
In my younger years while developing in the confinement of Windows, I would use a great peice of open source software called httrack. But now that Linux is exteremly easy and cheap to access (Less than a penny per hour at Digital Ocean), we can backup websites using wget.
Obviously you could read the man page, but I decided to create a bash script so all I have to do is enter the domain name and optionally the path to save the file, saving me from having to remember all the options.
Checkout my code on GitHub: