# Improving Water Efficiency in a Municipal Indoor Swimming-Pool Complex: A Case Study
## 3 Results
### Preliminary Analysis of the Viability of Filter Backwashing Reuse  
The average daily water consumption for swimming pool filter cleaning was 15.7 m\({}^{3}\) (competition pool) and 7.7 m\({}^{3}\) (learning pool). These filters (Table 1) are cleaned every two days. Therefore, the estimated annual water consumption for filter backwashing was 2818.8 m\({}^{3}\) and 1378.8 m\({}^{3}\), respectively, totaling 4197.6 m\({}^{3}\), which are discharged into the wastewater drainage network.  
The highest values for the TSS, turbidity, and free residual chlorine concentrations were observed in the samples collected during the first minute of the filter backwashing (first flux). In those collected in the third minute, a reduction between 10% and 20% occurred in the studied parameters. Concerning the TSS, the 2 and the 15 hour sedimentation reduced the amounts of suspended solids to be 60% and 80%, respectively. A similar trend for both the turbidity and the free residual chlorine was recorded. Nevertheless, the TSS, turbidity, and free chlorine samples exceeded the admissible values, except those submitted to 15 hour sedimentation (Table 5). The pH values were always within the admissible range. The total coliforms, fecal coliforms, and fecal streptococci were not detected.  
Considering a scenario including: (1) flushing cistern volume adjustment; (2) filter backwashing reuse to irrigate the lawn of the local football stadium; (3) the replacement  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Sample Sedimentation Time** & **Values (1,2,3)** \\ \hline \multirow{8}{*}{TSS (mg/L)} & No sedimentation (1 min) & 61.5 \\  & Sedimentation 2 h (1 min) & 24.5 \\  & Sedimentation 15 h (1 min) & 9.0 \\  & No sedimentation (3 min) & 49.5 \\  & Sedimentation 2 h (3 min) & 21.5 \\  & Sedimentation 15 h (3 min) & 10.0 \\ \hline \multirow{8}{*}{Turbidity (NTU)} & No sedimentation (1 min) & 36.1 \\  & Sedimentation 2 h (1 min) & 5.0 \\ \cline{1-1}  & Sedimentation 15 h (1 min) & 1.7 \\ \cline{1-1}  & No sedimentation (3 min) & 25.5 \\ \cline{1-1}  & Sedimentation 2 h (3 min) & 5.9 \\ \cline{1-1}  & Sedimentation 15 h (3 min) & 1.9 \\ \hline \multirow{8}{*}{Free residual chlorine (mg/L)} & No sedimentation (1 min) & 0.58 \\  & Sedimentation 2 h (1 min) & 0.12 \\ \cline{1-1}  & Sedimentation 15 h (1 min) & 0.02 \\ \cline{1-1}  & Sedimentation 2 h (3 min) & 0.11 \\ \cline{1-1}  & Sedimentation 15 h (3 min) & 0.02 \\ \hline \multirow{8}{*}{pH} & No sedimentation (1 min) & 6.7 \\ \cline{1-1}  & Sedimentation 2 h (1 min) & 7.1 \\ \cline{1-1}  & Sedimentation 15 h (1 min) & 7.8 \\ \cline{1-1}  & No sedimentation (3 min) & 6.8 \\ \cline{1-1}  & Sedimentation 2 h (3 min) & 6.4 \\ \cline{1-1}  & Sedimentation 15 h (3 min) & 7.8 \\ \hline \hline \end{tabular}  
* Flushing cistern quality requirement: TSS 10 mg/L; Turbidity 2 NTU [31]. 2 Invitation quality requirement: TSS 10 mg/L; Turbidity 2 NTU [31]. Irrigation of private gardens: for lawn irrigation, the same requirements were adopted. 3 Recommended limit: Free residual chlorine 0.2–0.6 mg/L [32; 33] pH: 6.5–9.0 [32].  
\end{table}
Table 5: TSS, turbidity, free chlorine, and pH values observed in 1 st and 3 rd minute. Filterbackwashed water samples were submitted to different sedimentation times.  
of showers; and (4) the replacement of the washbasin and kitchen taps, the water savings could reach 23.3%.