# Towards Sustainable Water Use in Two University Student Residences: A Case Study
## 3 Results and Discussion
### Implementation of Water-Saving Measures
Although this study did not address the seasonal variation in water consumption, the analysis of the water bills provided by the university's managers indicates that water consumption remains relatively constant throughout the year, with a sharp reduction during the summer vacation (August). This assumption is also corroborated by [10; 30]. Ref. [10] demonstrated that the reliability of RWHS in Aveiro University buildings (Portugal) during the summer months is not significantly affected. The water quality is another challenge to the RWHS's viability. Even though flushing cisterns can be replenished with non-potable rainwater, the water used in these devices has quality requirements [50]. Roof runoff entering the RWHS can be contaminated with several pollutants accumulated on footops during dry periods, affecting the harvested \begin{table}
\begin{tabular}{l c c c c} \hline  & **Scenario 1** & **Scenario 2** & **Scenario 1 * & **Scenario 2 * \\ \hline Total water consumption without measures (m\({}^{3}\)/year) & 318.8 & 318.8 & 1286.45 & 1286.45 \\ Predicted water consumption with measures (m\({}^{3}\)/year) & 286.32 & 244.94 & 1151.20 & 1020.05 \\ Predicted water saving (m\({}^{3}\)/year) and (\%) & 32.48 (10.19) & 73.86 (23.17) & 1352.5 (10.51) & 266.40 (20.71) \\ Predicted equipment costs (EUR) 1 & 2406.60 * & - & 2406.60 * & - \\ Annual water bill without measures (EUR) 2 & 1787.40 & 1787.40 & 7013.90 & 7013.90 \\ Predicted annual water bill with measures (EUR) 2 & 1573.20 & 1348.10 & 6282.50 & 5564.70 \\ Annual water bill reduction (EUR) 2 & 214.20 & 439.30 & 731.40 & 1449.20 \\ Energy consumption without measures (kWh) 3 & 14,347.38 & - & 59,783.25 & - \\ Energy consumption with measures (kWh) 3 & 11,039.52 & - & 45,998.00 & - \\ Predicted energy saving (kWh) and (\%) & 3307.86 (23.06) & - & 13,785.25 (23.06) & - \\ Annual energy bill without measures (EUR) 4 & 1997.90 & - & 7602.38 & - \\ Predicted Annual energy bill with measures (EUR) 4 & 1537.29 & - & 5849.37 & - \\ Energy bill reduction (EUR) 4 & 460.61 & - & 1753.01 & - \\ Investment turnover (years) & 3.57 & - & 0.97 & - \\ \hline \end{tabular}  
* Residence with maximum occupancy; a price + VAT; 1 Scenario 1 devices. The maintenance costs were not considered because the IPB’s staff carry this out; 2 calculated according to the municipality’s water price estimation methodology; 3 total energy consumption by kitchen taps and showers considering all residents calculated according to Section 2.3. 4 Calculated according to the energy bills provided by the electricity company.  
\end{table} 
Table 6: Water and energy consumption and cost without and with water-saving measures and investment turnover in Residence II. water quality [51]. Therefore, it is necessary to dispose of at least the first rainwater after a long dry period (first flush), as recommended by [42], which can affect the amount of stored water. However, the main challenge associated with installing RWHS is the extended payback period. According to [41], this period can stretch up to 19 years. Coupled with the low water prices [52], university managers may perceive this investment as costly and unprofitable. Despite the RWHS's potential limitations, when making decisions concerning its installation, it is essential to consider the trade-off between these limitations and the positive environmental impacts [27; 28; 29; 47; 53; 54]. Additionally, there is a need for further research to understand the functionality of these systems, and the promotion of students, decision-makers, and citizen literacy regarding sustainable water use [55].