Joining water main layers

I have 4 layers, each describing a color coded Water Main in the city: Current, Abandoned, Reservoir, and Proposed. I want to combine them into one layer so that each line is a feature class. When a current line is abandoned (or any line's status is switched) I can just change the attribute, and the color will change on the map as well. I just think there isnt any point in having 4 layers all describing water mains, when i can have 1.

I think I need to join the layers, but im not certain if this is correct. Im sure this is a simple fix, I just want to be sure. Im still an expendable intern haha.