Where should turbidity samples commonly be collected from?

Collecting turbidity samples at representative source entry points is crucial for accurately assessing water quality. These entry points are where the untreated source water first enters the treatment process, allowing operators to determine the initial level of turbidity before any treatment is applied. This measurement is essential for evaluating the raw water quality and understanding how effective the treatment processes are in reducing turbidity levels.

Monitoring turbidity at this stage helps to identify potential issues with source water, such as sediment loading or seasonal changes affecting water clarity. Additionally, by knowing the turbidity levels at these entry points, operators can better adjust treatment processes to ensure the water meets regulatory standards and is safe for distribution.

In contrast, the other options focus on different stages of the water treatment and distribution process where turbidity levels can fluctuate due to treatment efficiency, distribution system conditions, or contaminants from consumer use, making them less optimal for evaluating the initial source water quality.