The Philadelphia Water Department (PWD) can apparently return "Invalid Reading" when accessing "gallons per day":

Although the web interface says "Invalid Reading" for Tuesday, July 15, 2025 in the above screenshot, this is not indicated in their exported (ChartData.csv) file. The export file includes that day as having had 0.0 gallons of "Consumption":

Access Code, Time Interval, Consumption, Units
123456789, 07/12/2025, 13.4649, Gallons
123456789, 07/13/2025, 19.4494, Gallons
123456789, 07/14/2025, 13.4649, Gallons
123456789, 07/15/2025, 0.0, Gallons
123456789, 07/16/2025, 32.1662, Gallons
123456789, 07/17/2025, 10.4727, Gallons

So unfortunately, there seems to be no way to detect "Invalid Reading" programmatically from within the export file.

Therefore, any day with an "Invalid Reading" will be stored in the database, returned, and displayed as if it had no usage (0 gallons) that day, for example: