# Improving Water Efficiency in a Municipal Indoor Swimming-Pool Complex: A Case Study
## 4 Discussion  
The approach discussed in this study showed that it is possible to promote a substantial increase in water efficiency in this facility by simply increasing the efficiency of water use for sanitary and hygienic purposes. As in other swimming pool facilities, the showers demonstrated the highest water consumption [1,8,9,19,34]. Therefore, the proposed measures, if implemented, will reduce the financial burden and increase the environmental benefits associated with water use. Herein, the energy consumption under the scope of the water-energy nexus was not evaluated. However, several authors describe large amounts of energy consumption due to excessive water use in residential or public buildings [1,6,7,35,36,37,38]. According to data obtained by [7], each cubic meter of water consumed implies the consumption of 1.115 kWh in the water supply system and the consumption of 0.818 kWh in drainage treatment and wastewater treatment processes, adding up to a total of 1.933 kWh. Therefore, assuming similar levels of energy consumption in the Braganca region, it is plausible to admit that the water consumption reductions predicted in each scenario would lead to energy savings in the public system ranging from around 2562.96 to 6532.52 kWh/year. Consequently, the turnover and the earnings for the different studied scenarios are monetarily and environmentally much higher than the estimates obtained herein. Indeed, implementing inexpensive and straightforward water efficiency measures (substituting showers and taps with more efficient devices) is also an essential step to improving energy efficiency while simultaneously reducing the waste of water, CO2, and other greenhouse gas emissions. The results concerning water consumption in pools (Table 2) are underestimates because they do not include the water losses caused by evaporation, swimmers exiting the pool, and water splashes. The authors of [34] demonstrated that an indoor heated 300 m\({}^{2}\) pool can lose 21,000 L of water per week through evaporation (water temperature: 28 \({}^{\circ}\)C, air temperature: 29 \({}^{\circ}\)C, and air humidity: 60%). Indeed, the water consumption in an indoor swimming pool, excluding sanitary and hygienic requirements, can reach 160 L/person per day, and the energy used is reported to be between 400 and 1600 kWh/m\({}^{2}\) of the usable area [9,34]. In general, indoor swimming pools use two types of energy sources: (1) thermal energy for showers, pool water, and space heating (the most significant portion of energy consumption); and (2) electricity to power water pumping systems, lighting systems, rotating equipment, air cooling, dehumidifying processes, and water treatment systems [19]). In Braganca swimming pools, natural gas boilers are the equipment used for producing hot water. According to information provided by the municipality concerning the period from 2018-2019, the mean annual value of natural gas consumption in the swimming pool's facilities was 719 KWh/m\({}^{2}\) (the data concerning electricity consumption were not available). The most frequent water and energy saving measure is the application of a cover over the water's surface during periods in which the facility is not in use, allowing the reduction of water evaporation [19] and the release of volatile disinfection by-products that negatively affect indoor air quality, often causing eye irritation or even asthma in users [11,39]. Additionally, this measure reduces air humidity, reducing the need for dehumidifying procedures and water reposition, which results in lower water and energy consumption levels. Efficiency measures affecting the filter flow rates, preventing good water mixing by creating zones in which water cannot circulate, should be avoided because of users' health and safety [11,40]. Regular swimming pool filter backwashing is unavoidable due to the need to remove the contaminants accumulated during the filtration process and to condition the filter beds for continued efficient operation [41].