The whole of it. You stated that most municipal water supplies aren't monitored for months at a time. This is extremely incorrect. The EPA-mandated quarterly report is a summary, not the entirety of samples collected. It would be dangerous and reckless not to monitor drinking water for months at a time.

E.g., Seattle explicitly states:

> We monitor your water 24 hours a day, 365 days a year. We test samples from the region between 10 and 100 times per day.

https://www.seattle.gov/Documents/Departments/SPU/Services/W... (PDF)

> To ensure the safety of our drinking water, SPU's water quality laboratory analyzes over 20,000 microbiological samples each year (more than 50 a day) and conducts chemical and physical monitoring daily, 365 days per year.

https://www.seattle.gov/utilities/your-services/water/water-...