## 2 Climate Change Impacts and Response Strategies in the Urban Environment
### Mitigation Strategies
Naturally, these results may vary significantly with the characteristics of the water supply and drainage systems, especially with regard to public systems, but it should be noted that the system in the Aveiro region presents one of the lowest public water system energy consumptions in Portugal, due to its characteristics (flat city, superficial abstractions, etc.). There are other studies that have been carried out about the relationship between water efficiency and energy efficiency in buildings [27; 28; 29] which reinforce the results of the above-mentioned study. However, it should be noted that the contribution of water efficiency in buildings to the reduction of energy consumption in public systems is generally neglected, but the study carried out in Aveiro showed that it can have a non-negligible value (around 13% in the case study). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Component of the Urban**} & \multicolumn{3}{c}{**Annual Energy Savings and CO\({}_{2}\) Reductions with the Use of Water-Efficient Products**} \\ \cline{2-6}  & **Per Person** & **Per Person** & **Per Family** & **Per Family** & **Percentage of** \\  & **(kWh)** & **(kg of CO\({}_{2}\))** & **(kWh)** & **(kg of CO\({}_{2}\))** & **the Total (\%)** \\ \hline Building system (only sanitary hot water heating) & 368 & 99.0 & 846 & 228.4 & 87.0 \\ \hline Public system of water supply & 32 & 8.6 & 74 & 19.9 & 13.0 \\ \hline Public system of drainage & & & & & \\ and treatment of wastewater & 23 & 6.2 & 53 & 14.3 & \\ \hline TOTAL & 423 & 113.8 & 973 & 262.6 & 100.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Estimated energy savings and CO\({}_{2}\) reductions with the use of water-efficient products in buildings. In Aveiro, energy consumption in the public networks was 1.98 kWh/m\({}^{3}\) (1.16 kWh/m\({}^{3}\) in the public water supply system, and 0.82 kWh/m\({}^{3}\) in the public system of drainage and treatment of wastewater) [26]. Based on these values, it is possible to draw some conclusions about the energy consumed by some water uses in buildings, even in situations where only cold water is used, and which are not obvious to consumers. For example, it allowed us to determine that the discharge of a 6-litre flushing cistern implied an energy consumption close to 12 Wh in the public water supply and drainage networks, equivalent to a common 3W LED lamp connected for 4 h.  
In general, the reuse of greywater and rainwater harvesting systems can also contribute to reducing the energy consumption. Indeed, as these systems reduce drinking water consumption in houses, they also reduce water flows and energy consumption in public networks. For example, based on the value of 1.16 kWh/m\({}^{3}\) and on an estimate of the daily consumption in flushing cisterns of 145.8 liters per house in Aveiro, we can conclude that the use of rainwater in toilets, as an alternative to the use of drinking water from the main water system, would allow for an energy saving in the public water supply network of about 62 kWh per house and per year. Although rainwater harvesting systems may demand a pressurization system in the building, the corresponding energy consumption is equal to or less than that which occurs when the supply derives from the public network. Compact installations for the direct reuse of greywater (toilett and washbasin combined, for example), reduce water consumption in buildings and also lead to saving water and energy. With regard to large installations for greywater reuse, when a centralized \"conventional\" treatment is employed to regenerate these effluents, we find that the energy consumed in the treatment makes the system \"neutral\" from an energy standpoint, i.e., the energy expended in treating greywater, about 1.8 kWh/m\({}^{3}\), is close to the energy saved in the urban water cycle.