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Taiwan experiences abundant rainfall, but faces significant water shortages, making rainwater harvesting (RWH) a potential alternative water source. Additionally, extreme rainfall events strain urban flood control systems, highlighting the need for integrated stormwater management. To address these challenges, Taiwan mandates stormwater detention (SWD) in new buildings. However, the current RWH and SWD systems are designed independently, with no combined design guidelines available. This study proposes three combined RWH and SWD systems, series, parallel, and enhanced parallel with a valve using a passive release mechanism. System performance was evaluated through short-term and long-term simulations. Short-term simulations were conducted to ensure the system's compliance with the domestic flood control design standards. These simulations assessed the peak flow mitigation and lag times for 5-, 10-, and 25-year design storms under four scenarios. Long-term simulations used historical rainfall data to analyze the differences in the combined systems and operational plans for continuous rainfall events. Three performance indicators—volumetric reliability, the stormwater retention ratio, and the stormwater detention ratio—were employed to assess water supply and the stormwater detention performance. The short-term simulation results revealed that the system performance was sensitive to the initial conditions. The series and parallel systems performed well, while the enhanced parallel system outperformed the others under specific initial conditions and valve operations. In contrast, long-term simulations revealed that the series and parallel systems achieved higher stormwater retention and a more stable performance than the enhanced parallel system. Among the three systems, the parallel system offers reduced installation space, lower costs, and easier maintenance, making it the recommended option for Taiwan. This study provides valuable guidance for designing combined RWH and SWD systems. [ABSTRACT FROM AUTHOR]

A water balance modeling method was developed and applied to assess the water flow impact on urban water systems and water consumption in buildings. The method is based on the computational tool Aquacycle and a case study applied in a city in Brazil. Some modifications have been made to Aquacycle, including using urban drainage and sewage structures commonly applied in Brazil and parameters closer to the Brazilian reality. Such structures are decentralized wastewater treatment systems, deep tubular wells, irregular urban networks, and covered tanks for storing rainwater. Also, an automatic rainwater harvesting system was considered for flood mitigation. The water balance proposed may also be used for a modular assessment approach in urban water systems, aiming to facilitate the application of life-cycle assessment. A case study also aimed to assess alternative water supply in buildings, including scenarios with and without rainwater harvesting. The most significant positive impacts of using rainwater in buildings were a decrease of almost 6% in stormwater runoff and a decrease of water consumption by around 30%. There is a substantial waste of water in the distribution process, which, although it favors groundwater recharge, can have a high impact when considering energy and chemical products consumption. All contributions obtained via modeling can be used to provide specific fluxes in each component that can be used for technical, financial, or environmental evaluations, such as life-cycle approaches, carbon footprint, and cost–benefit assessment. [ABSTRACT FROM AUTHOR]

Drought is a recurring disaster in several regions of Indonesia, often happening from April to September annually. During the dry season, a substantial reduction in rainfall leads to inadequate water supplies and drought. Drought significantly affects food crop output, water scarcity, and reduced water availability for daily necessities, disrupting everyday activities like bathing, washing, and cooking. Seraya Village, situated in Karangasem Regency, Bali Province, frequently faces drought conditions. Seraya, a settlement prone to drought, was officially designated as such by the Karangsem Regent by Regulation Number 36 of 2008, specifying the location of drought natural disasters in Seraya settlement, East Seraya, and West Seraya in the Karangasem District. This study aimed to compare the capacity of rainwater harvesting with the current home water demand in Seraya-Karangasem Village to determine the feasibility of using rainwater to address water shortages and avert drought. This study employs quantitative descriptive methods by analyzing primary data on the regional conditions and limits of the study area, along with secondary data on demographic (population), geographical, and rainfall data spanning a decade. The study revealed that the rainwater harvesting potential in Seraya Village, Karangasem District, was 254342191.15 liters per year, while the total water demand was 227660565 liters yearly. This resulted in excess harvested water amounting to 26681626.15 liters per year, 12% more than the total water needs. The excess amount of rainwater that may be harvested compared to the entire domestic water demand demonstrates the effective utilization of rainwater harvesting systems in preventing water shortages and droughts in Seraya-Karangasem Village.