SimpleBills works with many properties, a few of which have sub-metered utilities. Water is the most common sub-metered utility.
When your utility is sub-metered this means that there are individual transmitters for each unit or apartment that report the consumption. From time to time, there may not be an individual PDF available for a particular reading as we are not always provided with them. When there is a PDF available it will usually say "SimpleBills" or "NES" on the document.