The most accurate estimates of sewage flow are derived from:

The most accurate estimates of sewage flow are derived from annual water-meter readings due to their comprehensive nature. Annual readings provide a complete view of water usage over a full year, accounting for seasonal variations, fluctuations in usage patterns, and any irregularities in water consumption. This long-term data allows for a more precise assessment of the amount of sewage generated, as many factors influencing water usage, such as weather changes and outdoor activities, are balanced out over a year.

In contrast, quarterly or semiannual readings may miss significant variations that could occur between the intervals of measurement. They may not capture infrequent but high usage events or periods of low consumption that can skew estimates. Fixture units, while useful in estimating potential flow based on the type and number of fixtures in a building, do not provide actual usage data and can be less reliable without actual metered flow data. Therefore, annual water-meter readings are the most beneficial for an accurate estimation of sewage flow.