If you don’t have any GIS data yet, you must go to data collection first. You might need some GPS devices such as Trimble or Garmin. But you can also use following smartphone applications for data collection.
Both applications are free and open source, it is completely compatible to QGIS. However, I personally recomment to use QField which is more advanced and user friendly.
You can also have a look about nice case study of QField in rural water supply systems in Rwanda from here.
If you need some assists about data collection, please let me know.