An audit of Atlanta's Water and Sewer Department shows it is sitting on $3.9 million that should have been refunded to thousands of customers.

The amount was among 83 findings in a $500,000 audit of the Watershed Management Department ordered by the city council last year and delivered to the council on Wednesday.

The audit also showed that delinquent accounts total more than $50 million and the department fails to collect millions more every year.

Bills are based on estimates, rather than meter readings, for 10,000 accounts every month.

Council members said little during the six-hour presentation.