# Towards Sustainable Water Use in Two University Student Residences: A Case Study
## 3 Results and Discussion
### Implementation of Water-Saving Measures
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & **Scenario 1** & **Scenario 2** & **Scenario 1 *** & **Scenario 2 *** \\ \hline Total water consumption without measures (m\({}^{3}\)/year) & 325.67 & 325.67 & 835.54 & 835.54 \\ Predicted water consumption with measures (m\({}^{3}\)/year) and (\%) & 283.68 & 260.61 & 723.71 & 654.81 \\ Predicted water saving (m\({}^{3}\)/year) and (\%) & 41.99 (12.89) & 65.06 (19.98) & 111.83 (13.38) & 180.73 (21.63) \\ Predicted equipment costs (EUR) [1] & 1550.80 [FOOTNOTE:]Footnote : Residence with maximum occupancy, \({}^{2}\) 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.[ENDFOOTNOTE] & 1787.40 & 1787.40 & 4560.98 & 4560.98 \\ Predicted annual water bill with measures (EUR) [2] & 1558.86 & 1433.40 & 3950.45 & 3577.80 \\ Annual water bill reduction (EUR) [2] & 228.54 & 354.00 & 610.53 & 983.18 \\ Energy consumption without measures (kWh) [3] & 16,292.53 & - & 43,446.72 & - \\ Energy consumption with measures (kWh) [3] & 11,762.40 & - & 31,366.40 & - \\ Predicted energy saving (kWh) and (\%) & 4530.13 (27.80) & - & (27.80) & - \\ Annual energy bill without measures (EUR) [4] & 2268.77 & - & 6050.04 & - \\ Predicted Annual energy bill with measures (EUR) [4] & 1495.78 & - & 3988.73 & - \\ Energy bill reduction (EUR) [4] & 772.99 & - & 2061.31 & - \\ Investment turnover (years) & 1.55 & - & 0.58 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Water and energy consumption and cost without and with water-saving measures and investment turnover in Residence I. If Scenario 1 were implemented in the residences, there would be a 13% reduction in water consumption in Residence I and a 10% reduction in Residence II. The reduction in hot water consumption would lead to a decrease in annual electricity consumption of 27.8% and 23.06% in Residence I and II, respectively (Tables 5 and 6). Currently, the annual energy consumption per person for showers and kitchen tap water heating is 2715.42 kWh and 2391.33 kWh in Residence I and Residence II, respectively. With the proposed efficiency measures for both devices, the annual energy consumption per person is expected to decrease to 1960.40 kWh and 1839.92 kWh in Residence I and Residence II, respectively. In Portugal, generating 1 MWh of electrical energy emits 0.151 tCO\({}_{2}\) eq [48]. Therefore, 0.41 tCO\({}_{2}\) eq/year/device/person and 0.36 tCO\({}_{2}\) eq/year/device/person are produced in Residence I and Residence II, respectively. If the measures were implemented, emissions would decrease to 0.30 tCO\({}_{2}\) eq and 0.28 tCO\({}_{2}\) eq in Residence I and Residence II, respectively. Therefore, the present research demonstrates that investing in water efficiency, particularly in water-efficient devices, has the potential to be highly viable in both financial and environmental terms. The short payback period and low initial investment suggest that investing in water-efficient solutions is an attractive and achievable option. Thus, water savings for Residence I could reach around 20.0%, while in Residence II, only Scenario 2 could increase savings by up to 23.2%. The combination of consumption reduction measures with the implementation of RWHS mitigates the effects of low rainfall during the summer period. The expected irregularity of precipitation in the region [35; 49], which may be exacerbated during prolonged droughts or by intense, short-term rainfall, presents a challenge to the sustainability and resilience of these systems. However, it is believed that continued use will remain viable for saving potable water in applications where drinking water is not required.