The effect of filter backwash on the efficiency of first-stage sand-biological activated carbon (BAC) filters was evaluated by comparing, in first-stage sand-BAC filters, concentrations of ammonia, biodegradable dissolved organic carbon, aldehydes, and oxalate. These concentrations were measured before and after filter backwash. Filter position (first-stage sand-BAC filters versus second-stage BAC filters) was also studied to understand how floes and particle accumulation influenced the efficiency of the first-stage sand-BAC filter. A first-stage sand-anthracite filter operated under similar hydraulic conditions and effluent turbidity acted as a reference. Filter backwash improved the efficiency of sand-BAC filters, especially in cold water sources. However, both filters produced similar water quality. First-stage sand-anthracite filters did not adequately remove biodegradable organic matter and ammonia.