Do I Have a Loop?
A "loop" is a pre-plumbed item that may have been installed when your home was built. Most homebuilders charge additional for the loop, and it is usually located near your water heater. Pictured below are pictures of a typical "loop" and "full line".
If you do not have an existing loop, it will be necessary to connect to the main water line on the outside of your home, run plumbing to the location of the water softener, and then back to the water main. This creates a "loop". There can be many factors involved that will affect your options for the location where the water softener can go. These include location of the main water line, attic access, single or two story home, walkways, and other considerations.