Draw them as line assets on the water system, in the Surveyor app or in the Portal, or import the pipe data you already hold. Once pipes carry attributes such as diameter, material and age, they support analysis rather than only appearing on a map.
Video: Pipe mapping webinar on YouTube
A pipe drawn on a map is worth very little by itself. A pipe with a diameter, a material and an installation date is what lets a utility argue where non-revenue water is being lost, plan replacement by age rather than by complaint, and cost a rehabilitation honestly. Most utilities already hold some of this in a GIS file and can import it instead of resurveying.