Performance Of Rainwater Harvesting Systems Research Articles

The performance of rainwater harvesting systems in the context of deep uncertainties

The performance of rainwater harvesting systems in the context of deep uncertainties

StRaWHAT: A stochastic rainwater harvesting assessment tool for direct quantification of rainwater harvesting system performance

Rainwater harvesting (RWH) contributes to reduced flooding and relief of demand on water supply systems and is instrumental in sustainable development. The conventional analytical probabilistic approach for RWH has a limitation of requiring an assumption of the initial storage condition which may cause overestimation or underestimation of the system's performance. By deriving the average storage volume of the RWH tank to get rid of such an assumption, a stochastic rainwater harvesting assessment tool (StRaWHAT) which is comprised of a set of closed-form analytical equations was developed and proposed for use in directly quantifying the hydrological performance statistics of RWH systems. The accuracy of StRaWHAT was verified by comparing its results with those obtained from continuous simulations based on mass balance principles for a large number of design scenarios with different climate conditions (6 cities in China and the US), storage capacities (1–20 m3) and water use rates (0.5, 1, 1.5 or 2 m3/day). Close agreements (NSE = 0.984, RMSE = 0.022, and CORR = 0.995) between StRaWHAT and continuous simulation results illustrated that StRaWHAT can provide accurate results for all types of system configurations. Extensive example case studies were carried out for RWH systems located in six cities in China and the U.S. Different types of applications were also illustrated. Overall, the proposed StRaWHAT was proved to be a computationally efficient and ease-to-use tool for directly assessing the hydrological performance of RWH systems.

Assessing the benefits of real-time control to enhance rainwater harvesting at a building in Cape Town, South Africa

In the period 2015–2017, the City of Cape Town, South Africa, faced the possibility of taps running dry due to a prolonged drought. To mitigate the impacts of water scarcity, many households installed rainwater tanks to harvest water to use for non-potable purposes such as toilet flushing and washing. The installation of the rainwater tanks was mainly arbitrary, in response to perceived impact of water scarcity rather than a systematic needs assessment. This study was thus undertaken to determine the available opportunity to optimise the use of these rainwater tanks using real-time control (RTC) techniques. Many studies have demonstrated the potential of rainwater harvesting (RWH) systems to supplement potable water supply and minimize stormwater flows to downstream drainage networks. RTC technology can be used to enhance the performance of RWH systems in achieving these two objectives, by receiving a rainfall forecast and initiating pre-storm release in real time. In this study, RTC was applied on the RWH system at the New Engineering Building, University of Cape Town (UCT) to enhance water supply and increase rainwater retention period. The performance with RTC was compared with the conventional management of the RWH system. It was determined that RWH with RTC technology was generally superior in simultaneously achieving water supply and rainwater retention benefits compared to the conventional management approach. RTC provides an active operation which optimizes the performance of the system across varying conditions but requires an assiduous management process designed to meet set objectives. It was concluded that the active release mechanism employing RTC exhibited great potential; the system opens up the possibility of delivering a more robust and reliable system due to its ability to provide failure detection and centralised control. The system can readily be adapted to variation of local climatic conditions in the short and long term.

Influence of rainfall time series indicators on the performance of residential rainwater harvesting systems

Despite having abundant water sources, some Brazilian regions are likely to face water scarcity within the following decades. In this sense, rainwater harvesting (RWH) systems are considered viable solutions. This study evaluates the influence of rainfall time series indicators on the tank sizes, volumetric reliability and potential for potable water savings in residential buildings in Brazil. The study aimed to determine the most suitable rainfall conditions for RWH systems design. RWH systems were simulated for 27 Brazilian cities considering a daily water balance model. Total water demands and rainfall time series were considered for each city, and RWH-relevant indicators characterised each time series. Generally, cities with higher rainfall availability required smaller tank sizes and yielded greater volumetric reliabilities and potential for potable water savings. Cluster analysis was also used to investigate if similar rainfall patterns generate similar simulation results. Euclidean distance criteria grouped similar time series into ten clustering schemes. Coefficients of variation for tank sizes decreased within each scenario as more clusters were used, i.e. this method is feasible to design rainwater storage tanks. The remaining performance indicators did not show significant variation among the tested clustering scenarios. Similarity analysis resulted in increasingly similar results within each group as the clustering became more refined. As the main conclusion, correlation analysis presented the Seasonality index and indicators related to dry periods as the most influential towards the performance of RWH systems.

Reliability and economic assessment of rainwater harvesting systems for dairy production

The need for rainwater harvesting is continuously growing as a supplement to other water sources and the operation and maintenance costs remain low after the initial investment. The daily water balance method was used to determine the optimal rainwater harvesting tank size. Princeton Global Forcing (PGF) data gridded at (0.25° × 0.25°) is used after comparison with observed data. Correlations between PGF and observed stations varied by under or overestimating the precipitation. PGF series could ably reproduce observed rainfall, hence were used. The optimum water tank size varies based on the collection area, climatic conditions, and water pricing. According to the results, reliability is higher for larger rainwater tank sizes and higher for larger collections areas. Areas that receive more rainfall have higher reliabilities and require smaller tank sizes. Meeting 100% reliabilities requires collection areas greater than 500 m2 for demand of 750 L/day. Reliability was investigated for different tank volumes and an insignificant increase in reliability was observed for tank sizes greater than 50 m3. A roof collection area of at least 250 m2 and a tank size of 120 m3 and above is recommended to achieve more than 50% reliability. Installation of RWH systems is viable with a payback period of fewer than 4 years. The payback period is shorter for areas that receive high rainfall. The results in this study serve as a tool for comparison with other studies on evaluating the performance of rainwater harvesting systems and the possibility of using RWH systems beyond domestic and irrigation purposes.

Integrated Water Resource Management: Rethinking the Contribution of Rainwater Harvesting

Rainwater harvesting (RWH) is generally perceived as a promising cost-effective alternative water resource for potable and non-potable uses (water augmentation) and for reducing flood risks. The performance of RWH systems has been evaluated for various purposes over the past few decades. These systems certainly provide economic, environmental, and technological benefits of water uses. However, regarding RWH just as an effective alternative water supply to deal with the water scarcity is a mistake. The present communication advocates for a systematic RWH and partial infiltration wherever and whenever rain falls. By doing so, the detrimental effects of flooding are reduced, groundwater is recharged, water for agriculture and livestock is stored, and conventional water sources are saved. In other words, RWH should be at the heart of water management worldwide. The realization of this goal is easy even under low-resource situations, as infiltration pits and small dams can be constructed with local skills and materials.

Dynamic modelling of rainwater harvesting with green roofs in university buildings

University buildings may contribute significantly to the urban demand of potable water, particularly in small and medium communities with large universities. In this regard, alternative sources of water supply contribute to minimizing the pressure on natural resources. This paper investigates the applicability of rainwater harvesting (RWH) systems to partially compensate the daily non-potable water demand in university buildings. The traditional daily water balance model was improved to enhance the accuracy of the performance analysis and design optimization of the RWH system by accounting for consumption and runoff variability. The novel algorithm was tested using real daily water consumption data for two university buildings located in Portugal. In addition, different scenarios were evaluated combing RWH systems with extensive green roofs and different runoff distributions over time. The findings indicate that the use of real daily water consumption data instead of average values influences the final results, especially in buildings with fluctuating water consumption patterns over time up to 11%. Regarding the runoff coefficient, it was verified that variable values are recommended compared to the average values. Runoff variability associated with the installation of green roofs was found to decrease RWH system performance due to reduced stormwater runoff. However, the scenario with 50% of the catchment area covered by extensive green roofs showed promising results, decreasing the potential water saving less than 6% and increasing the volume of retained water by almost 15%.

Optimization of rainwater harvesting system design for smallholder irrigation farmers in Kenya: a review

Abstract The adverse effects of climate change on agriculture have been felt across the globe. Smallholder farmers in sub-Sahara Africa are particularly more vulnerable to the effects of climate change leading to loss of income and livelihood thus affecting global food security. Rainwater harvesting (RWH) is emerging as a viable option to mitigate the negative effects of climate change by supporting rain-fed agriculture through supplemental irrigation. However, smallholder farmers are still grappling with a myriad of challenges hindering them from reaping the benefits of their investment in RWH systems. This review explores some of the factors behind the poor performance of RWH systems in Kenya and also seeks to suggest techniques that can be applied to optimize the design parameters for improved performance and the adoption of RWH systems. According to the review, RWH has the potential to mitigate the adverse effects of climate change among smallholder farmers. It allows for crop production beyond the growing season through supplemental irrigation. However, their impacts have been minimal due to the consistent poor performance of RWH systems. This is attributed to inefficiencies in design and construction brought about by lack of required technical skills among RWH system designers and implementers. Proper design and implementation are therefore paramount for better performance and adoption of RWH systems in the region. This will ensure that RWH systems are reliable, technically and economically feasible as well as possess a desirable water-saving efficiency.

Influence of rainfall and design criteria on performance of rainwater harvesting systems placed in different Brazilian climatological conditions

ABSTRACT Using rainwater harvesting (RWH) system is influenced by socioeconomic, environmental and technical factors. This work presents as analysis of the influence of the rainfall time series characteristics and design criteria on RWH performance of five Brazilian capitals with different climatic characteristic: Goiânia, João Pessoa, Manaus, Porto Alegre and São Paulo. The analysis combined different rooftop areas, storage volumes and the indoor and outdoor demands. Rainfall temporal discretization and the types of demands were the most important characteristics when assessing RWH reliability. Daily rainfall data were suitable for sizing the RWH, the time series length influenced the sizing of larger storage volumes, and the RWH efficiency was not significantly affected by the first-flush. Toilet flushing and the irrigation demands had the greatest impact on RWH performance. The greatest potentials for the implementation of RWH were observed for Porto Alegre, because of well distributed rainfall throughout the year, and for Manaus owing to higher annual volumes of precipitation. These results highlight relevant aspects that must be observed during the conception and design of RWH, complementing the guidelines provided in the Brazilian technical standards.

Impacts of rainfall change on stormwater control and water saving performance of rainwater harvesting systems

Rainwater harvesting is widely implemented to deal with urban water scarcity and stormwater control issues. In the context of climate change, however, the impacts of rainfall change on rainwater harvesting systems (RHS) are still unknown in many regions. In this study, effects of rainfall change on both water saving and stormwater control performance of RHS across six cities in different climatic zones of Pakistan were investigated and location-specific and adaptive measures to mitigate the negative impacts of rainfall change on RHS were proposed. The commonly defined “dry gets drier, wet gets wetter” rainfall change pattern is not retained in the cities. Water saving performance of RHS is positively affected by increasing trend of rainfall at Khanpur and Peshawar, whereas negatively affected by rainfall decreases at Zhob and Murree. Conversely, increasing trend of rainfall is non-beneficial for stormwater control at Khanpur and Peshawar but rainfall decreases are beneficial at Zhob and Murree. Islamabad and Lahore do not have notable changes in performance of RHS due to the non-significant changing trends in rainfall. The impacts of rainfall change on performance of RHS are dependent on not only the trends and extents of local rainfall change, but also tank sizes and water demands. At Khanpur and Murree, the negative impacts of rainfall change on performance of RHS can be resolved by enlarging tank sizes. At Zhob and Peshawar, however, adjusting contributing areas or water demands should also be considered. Therefore, location-specific and adaptive measures should be adopted for RHS to accommodate rainfall change.

Water saving potential and economic viability assessment of rainwater harvesting system for four different climatic regions in China

Abstract Rainwater is one of the most promising alternative water sources. However, the financial outcomes of the rainwater harvesting (RWH) systems are not always assured as economic performance of RWH systems vary greatly under different climatic conditions.This paper investigates reliability, water saving and benefit-cost ratio of an RWH system with different storage tanks and under three distinct climatic conditions (i.e., wet, average and dry year) at four cities in China. It was found that for a standard building (1,600 m2 roof having 560 people), the rainwater supply reliability varies significantly (3.85–20.55%) across four cities. It was found that Guangzhou (South China) always achieves the highest reliability, greatest annual water saving and highest benefit-cost ratio under three distinct climate conditions. By contrast, Beijing (North China) is mostly ranked as having the lowest one. These findings are well in line with the historical annual precipitation in these regions. Also, it was found that across these four regions, it was not possible for a RWH system to achieve a benefit-cost ratio higher than 1.0. These findings indicate that the RWH systems in most regions of China are currently economically unfeasible without government subsidies.

The effect of climate change on domestic Rainwater Harvesting

One of the main strategies that are being applied to improve the efficiency of water consumption in buildings is the use of non-potable water for pavement washing, toilet flushing, irrigation, and others. According to several guidelines, the design and assessment of a Rainwater Harvesting System (RWHS) should be made using recent official records of precipitation. However, there is not an indication whether historical or future projections should be used, leaving space for the designer to choose. This article presents the study of RWHS in southern Europe, namely in Portugal, considering two case studies (a dwelling in Oporto and an apartment in Vila Real). The main goal was to explore the impacts that climate change will have on these systems and, for that purpose, a daily simulation using future rainfall data was performed for both cases considering two scenarios: RCP 4.5 which is more optimistic, and RCP 8.5 which is more pessimistic. The RWHS in Oporto showed a better performance in the future decades, comparing with simulations based on recent decades, for both scenarios. However, the savings will not have a significant variation (less than 5 €/year). In the future, this system will provide around 47 (±2.4) m3 of rainwater per year to the selected non-potable purposes, leading to savings of around 66 (±3.3) €/year. Vila Real case study also revealed a slight improvement of the system's efficiency in the future decades but the results for rainwater collected and used are so similar to the recent ones that it can be concluded that the performance will be sustained. This system will provide around 50 (±2.5) m3 of rainwater per year to the selected non-potable purposes, leading to savings of around 200 (±10.2) €/year. It can be concluded that there will be no significant changes in RWHS performance in the future, in the studied areas.

Technical and financial feasibility of rainwater harvesting systems in public buildings in Amazon, Brazil

Even with a multitude of studies that model and make possible the use of Rainwater harvesting (RWH) systems in particular and commercial contexts, there is still a gap in knowledge regarding the performance of these systems in public buildings. Thus, the objective was to evaluate the installation of a RWH system in two public higher education buildings at the Federal University of Pará (UFPA), which have different catchment areas, water tariffs, non-potable water demand and number of users. The simulation of the rainwater catchment system and the financial analysis were performed with the Neptune 4.0 software. In the first building evaluated, which does not buy water from the concessionaire, has the largest catchment area and the highest demand for non-potable water, there is a potential for an average monthly reduction of 80% in drinking water for less noble purposes. In this case, the project proved to be unfeasible with no financial return on the costs of implementation and maintenance within the assessed time. In the second building, which buys water from the concessionaire and has the lowest non-potable demand and roof area, it would be possible to obtain an average monthly reduction of 87% in demand. In this building, the installation is viable, with a 10-year payback. Thus, it is possible to conclude that public buildings with small coverage areas can have a good water saving potential, as long as the demand is low and the climatic conditions are favorable to the use of rainwater. The results found in this research can serve as a comparison tool for other studies that aim to evaluate the performance of RWH systems in public buildings in other countries.

Assessing reliability of rainwater harvesting systems for meeting water demands in different climatic zones of Iran

Assessing the performance of rainwater harvesting systems, which is one of the effective ways to cope with the water shortage crisis, leads to better management of these systems. In this paper, the reliability of rainwater harvesting systems and the overflow ratio of storage tanks were investigated for different climatic conditions, different volumes of tanks, and different roof areas. The results indicated that in the cities of Rasht, Sari, Tabriz, and Yazd, using a 10-m3 tank, non-potable water needs of a four-person family can be supplied from a 100-m2 roof area for 67.3, 42.98, 12.07, and 1.35% of the days during a year. Further, if a 1-m3 tank is used in Rasht, 50.67% of the total harvested water will be overflowed, which would decrease to 19.21% if the 10-m3 tank is replaced. For Tabriz, the ratio of overflow from the 5-m3 tank was zero, but for the city of Sari, even with use of a 10-m3 tank, 0.73% overflow occurred. In addition, for Yazd city, using a 1-m3 tank, an overflow of 48.4% occurred, but when the volume of the tank was increased to 2 m3, there was no overflow. For the city of Tabriz, the ratio of overflow from the 5-m3 tank was zero, but for the city of Sari, even using a 10-m3 tank, 0.73% overflow occurred. For a constant volume of storage, as long as the average rainfall of the area was high, the ratio of overflow was also elevated. The ratio of overflow, from the highest to the lowest, was related to the temperate climate of the Caspian Sea and the pseudo-Mediterranean climate, moderate and humid climate, mountainous climate, and desert hot and dry climate, respectively.

Potential of harvesting rainwater from vertical surfaces

The water supply chain is under increasing stress as urbanization and population growth is driving more and more people to move to cities. An increasing amount of city planners are now looking for alternative water resources, rainwater being one of them. There are multiple benefits to on-site water collection, storage and use, as proven by multiple published studies and successful projects around the world; however, rainwater harvesting (RWH) has remained a niche technique, not seen as part of the mainstream. One of the reasons for this is that, traditionally, rainwater has only been collected from rooves and other horizontal surfaces, and then transferred and stored in various subsurface holding tanks. This method of RWH is dated and not very effective. Furthermore, rainwater is one of the purest water sources, but when collected from horizontal surfaces, it gets polluted with particles that have settled on those surfaces. As a result, RWH in this way can be used only for specific purposes. In order to fully utilize this natural resource, to enable the creation of sustainable cities, we must devise a new method for collecting rainwater. One aspect of RWH that has not yet been deeply explored is collecting it from vertical surfaces. Although some abstract studies have already been conducted, concerning water runoff from vertical surfaces, no studies have evaluated the possibility of harvesting and using such water. In this paper, the impacts of different sets of conditions and variables on the performance of RWH systems mounted on vertical surfaces, such as building facades, are compared. In addition, this study aimed to evaluate the potential of such systems to be used in real-world projects around the globe. To accurately measure collected rainwater, an experimental stand was constructed. This stand consisted of a mechanism that allowed the water-collecting surface and its parameters to be changed, whilst also measuring various aspects of the weather and the amount of water that was successfully harvested. The experiments were conducted in both a controlled environment (laboratory) and under real (natural) conditions.The results of this study provide a more accurate evaluation of how vertical RWH systems can be implemented in real-life projects around the globe, and show how natural conditions and the surfaces used can change the effectiveness of RWH. DOI: http://dx.doi.org/10.5755/j01.sace.23.2.21606

Analysis and Modelling of Stormwater Volume Control Performance of Rainwater Harvesting Systems in Four Climatic Zones of China

Rainwater harvesting has been widely used to alleviate urban water scarcity and waterlogging problems. In this study, a water balance model is developed to continuously simulate the long-term (57 to 65 years) stormwater capture efficiency of rainwater harvesting systems for three water demand scenarios at four cities across four climatic zones of China. The impacts of the “yield after spillage” (YAS) and “yield before spillage” (YBS) operating algorithms, climatic conditions, and storage and demand fractions on stormwater capture efficiency of rainwater harvesting systems are analyzed. The YAS algorithm, compared with the YBS, results in more conservative estimations of stormwater capture efficiency of rainwater harvesting systems with relatively small storage tanks (e.g., ≤50 m3). The difference between stormwater capture efficiency calculated using the YBS and YAS algorithms can be remedied by increasing storage capacity and reduced by decreasing water demand rates. Higher stormwater capture efficiency can be achieved for rainwater harvesting systems with higher storage and demand fractions and located in regions with less rainfall. However, the lager variations in annual rainfall in arid zones may lead to unstable stormwater management performance of rainwater harvesting systems. The impacts of storage and demand fractions on stormwater capture efficiency of rainwater harvesting systems are interactive and dependent on climatic conditions. Based on the relationships among storage capacity, contributing area, water demand, and stormwater capture efficiency of rainwater harvesting systems, easy-to-use equations are proposed for the hydrologic design of rainwater harvesting systems to meet specific stormwater control requirements at the four cities.

Improving the Multi-Objective Performance of Rainwater Harvesting Systems Using Real-Time Control Technology

Many studies have identified the potential of rainwater harvesting (RWH) systems to simultaneously augment potable water supply and reduce delivery of uncontrolled stormwater flows to downstream drainage networks. Potentially, such systems could also play a role in the controlled delivery of water to urban streams in ways which mimic baseflows. The performance of RWH systems to achieve these three objectives could be enhanced using Real-Time Control (RTC) technology to receive rainfall forecasts and initiate pre-storm release in real time, although few studies have explored such potential. We used continuous simulation to model the ability of a range of allotment-scale RWH systems to simultaneously deliver: (i) water supply; (ii) stormwater retention; and (iii) baseflow restoration. We compared the performance of RWH systems with RTC technology to conventional RWH systems and also systems designed with a passive baseflow release, rather than the active (RTC) configuration. We found that RWH systems employing RTC technology were generally superior in simultaneously achieving water supply, stormwater retention and baseflow restoration benefits compared with the other types of system tested. The active operation provided by RTC allows the system to perform optimally across a wider range of climatic conditions, but needs to be carefully designed. We conclude that the active release mechanism employing RTC technology exhibits great promise; its ability to provide centralised control and failure detection also opens the possibility of delivering a more reliable rainwater harvesting system, which can be readily adapted to varying climate over both the short and long term.

Proposal of simple and reasonable method for design of rainwater harvesting system from limited rainfall data

Recently, rainwater harvesting (RWH) is gaining interest as an alternative source of safe drinking water especially in developing countries. Getting a detailed and suitable rainfall data to have a good design of RWH system is a challenge in developing countries. In RWH system performance predictions, direct use of monthly rainfall data may lead to considerable error instead of using daily rainfall data. This paper proposes a simple and reasonable design method of rainwater harvesting system from available limited data like monthly rainfall data, which can achieve negligible error and conservative predictions. A RWH model that employs the designed rainfall which generates daily rainfall for each month with distribution of uniformly number of wet days in the last days of month as its input gives performance predictions quite similar to that of using actual daily rainfall.

Evaluation of the Performance of Rainwater Harvesting Systems for Domestic Use in Tlalpan, Mexico City

Rainwater harvesting (RWH) as an alternative means of providing water in domestic contexts, is viewed as an effective supply option worldwide. In Mexico City, the water situation is critical and the provision of water services to the population represents a formidable challenge for the city’s water utilities. The main objective of this study is to evaluate the potential for RWH to supply domestic properties in Tlalpan, 1 of 16 delegations in the city with one of the highest percentages of homes unconnected to the distribution network. Results show RWH can meet 88% of household water demand during the 6 month wet season, with an annual saving of 55%. Modelling a World Health Organisation minimum demand of 20 l/p/d as a means of resilience management in the event of a water crisis, 6-month and annual savings were 99% and 80% respectively. The minimum tank size to achieve wet season savings of 90% was 6m3 in two precipitation bands and tank sizes of 13,000 – 17,000L were sufficient in 3 out of 4 to prevent overspill. The report concludes RWH is a viable method of providing water in the south of the city and should be part of an integrated water management solution.

A dimensionless approach for the urban-scale evaluation of domestic rainwater harvesting systems for toilet flushing and garden irrigation

A dimensionless methodology to evaluate the water saving obtainable from large-scale implementation of domestic rain water harvesting (RWH) systems in urban areas is presented. The methodology combines the use of regressive relationships for water saving evaluation based on the results of the dimensionless rainwater tank water balance and of catchment-wide information obtained from geospatial databases. The adopted RWH scheme included internal use of rainwater for toilet flushing and external use for garden irrigation. An application to a portion of the city of Rome, Italy showed the methodology to allow systematic and accurate evaluation of RWH system performance at the selected urban scale. Results pointed out high water saving potential for toilet flushing ranging between 38–65% for tank sizes within 1–50 m3. Furthermore, more than one third of the systems provided water saving benefit for irrigation larger than 20% by using a 50 m3 tank.