Studies on the Recovery of Wash Water from Swimming Pool Filters and Their Characteristics—A Case Study

Filter wash water (FWW) from public swimming pools is a recoverable resource, yet full-scale evidence on safe on-site reuse with documented economics is scarce. We evaluated a full-scale integrated recovery unit (SOWA) installed at an indoor public pool. The SOWA system—sedimentation, granular filtration operated at a hydraulic loading rate (HLR) of 7.5–10 m3 m−2 h−1, ultrafiltration, and chlorine-dioxide (ClO2) disinfection—was monitored for physicochemical and microbiological performance. Turbidity decreased from 23.1 nephelometric turbidity units (NTU) to 0.25 NTU; chemical oxygen demand, reported as the permanganate index (COD_Mn), fell from 10.4 to 1.6 mg O2 L−1; and total microbial count declined from 1.6 × 104 to 30 colony-forming units per millilitre (CFU mL−1). Indicator organisms (Escherichia coli, Intestinal enterococci and Pseudomonas aeruginosa) were not detected, and all quality criteria complied with national standards. At the Olender facility, monthly freshwater use dropped from 1700 to 1000 m3 after 24/7 SOWA operation, while combined chlorine was maintained at 0.12 mg Cl2/L and no issues with chloroform were observed. The unit recovered 4.7 m3 h−1 of FWW for non-potable uses. According to manufacturer catalogue data, the recovery process can reach up to 96%, enabling annual savings up to ~EUR 9000 and a payback of ~2 years under favourable tariffs and loads. Our outcomes are consistent with independent full-scale reuse trains (e.g., ultrafiltration/reverse osmosis) and with disinfection-by-product control strategies reported in the literature, and they align with international guidance for swimming-pool water reuse. This study provides a rare, end-to-end implementation at full scale, documenting continuous operation, verified microbial safety, regulatory compliance, quantified water and cost savings, and site-specific economics for a compact, multi-barrier FBW recovery system that can be directly transferred to similar facilities.