Investment Feasibility Analysis of Rainwater Use in Residences

This paper presents an investment feasibility analysis of rainwater harvesting systems for the residential sector in Santa Catarina State, southern Brazil. Five towns were selected for the analysis. Daily rainfall data, average water consumption, rainwater tank costs, water pump costs, and water, sewage and electricity tariffs were obtained for the five towns. Different values for the roof area, number of residents, potable water demand, and rainwater demand were analysed. The rainwater tank capacities were estimated using the Netuno computer programme. The investment feasibility analysis was performed considering the ideal lower tank capacity, as well as capacities smaller and larger than the ideal. Such capacities were obtained according to a variation of six months in the payback period. It was observed that the ideal tank capacity can be conservative for high rainwater demands. In such cases, an investment feasibility analysis should be performed in order to obtain a more appropriate tank capacity. The main conclusion is that rainwater usage is economically feasible for most cases; and the higher the rainwater demand, the higher the feasibility.     

Assessment of Potable Water Savings in Office Buildings Considering Embodied Energy

The objective of this article is to assess the potential for potable water savings in office buildings located in Florianópolis, southern Brazil. The embodied energy of four alternatives to reduce potable water demand, i.e., rainwater harvesting, greywater reuse, dual-flush toilets and water-saving taps, was also assessed. The analyses took into account the potable water end-uses for ten buildings. The potential for potable water savings by using rainwater, as well as, the rainwater tank sizing were estimated using computer simulation. As for greywater reuse, it was considered that greywater from lavatory taps could be treated and reused to flush toilets. The potential for potable water savings by using water-saving plumbing fixtures was estimated by considering the replacement of toilets and taps. In order to estimate the embodied energy in the main components, each system was dimensioned and embodied energy indices were applied. The main result is that the potential for potable water savings by using dual-flush toilets ranges from 21.6 % to 57.4 %; by reusing greywater, it ranges from 6.8 % to 38.4 %; by using rainwater, it ranges from 6.1 % to 21.2 %; by using water-saving taps it ranges from 2.7 % to 15.4 %. However, by considering the embodied energy, the average for the ten buildings indicates that dual-flush toilets are the best choice as it is possible to obtain water savings of 5.50 m³/month per GJ of embodied energy, followed, respectively, by water-saving taps, greywater reuse and rainwater usage. The main conclusion is that the assessment of embodied energy should be considered when evaluating potable water savings in buildings as it helps to identify the best alternatives to save more water while causing less environmental impact.     

Impact of El Niño and Climate Change on Rainwater Harvesting in a Caribbean State

The water situation of the Pusey district in St Catherine parish of Jamaica is acute because of the district’s hilly terrains which made connections to centralised public water supply difficult. Residents depend on rainwater harvesting (RWH) systems to meet potable needs, like many other catchments across Jamaica. Rainwater collecting practices and water use habits of the residents were surveyed and the present and future RWH capacity was evaluated using the available 18 years (1996 to 2013) rainfall data and downscaled PRECIS model A2 and B2 climate change scenarios. In addition, the effect of El Niño episodes on rainfall patterns was evaluated. The coefficients of variations for annual rainfall were found to be higher for the El Niño years than in normal years. In two of the El Niño years (1997 and 2009), rainwater harvesting capacity is negatively impacted as rainfall annual total is (42 % and 34 %) lesser than the average annual rainfall. The ability of RWH to meet potable needs in 2030s and 2050s will be reduced based on predicted shorter intense showers and frequent dry spells. A storage tank of 2.5 to 4.0 m³ per household (4 persons) is proposed to meet water demand during the maximum consecutive dry days, and January and February water shortage periods. Design of efficient RWH systems and provision of government subsidy on storage tanks will enable the residents to capture more rainwater to meet their daily domestic needs.     

基于线性规划法的屋面雨水箱容积优化模型

屋面雨水收集系统中最重要的可变参数是水箱容积,影响水箱优化容积的因素包括降雨数据、屋顶汇水面积、居民人数以及用水量等。采用线性规划法构建了对屋面雨水收集系统水箱体积的优化模型,以整个雨水系统寿命周期内的可变经济收益最大化作为目标函数,确定约束条件,并以南昌市为例进行模拟。模拟结果表明:不受市场调控的过低水价会使系统没有经济效益;屋顶汇水面积和月用水量是水箱优化容积的限制因素,在住宅楼中一般是屋顶汇水面积;在高层建筑和商业建筑上设置屋面雨水收集系统的经济效益会更高。     

Performance Analysis of a Communal Residential Rainwater System for Potable Supply: A Case Study in Brisbane, Australia

Cities in developed countries have increasingly adopted rainwater tanks as an alternative water source over the last 15 years. The rapid uptake of rainwater tanks has been driven by the need to reduce demand for centralised water services that are under pressure to adapt to population growth and climate change impacts. Rainwater tanks are part of integrated urban water management approach that considers the whole water cycle to provide water services on a fit for purpose basis that minimises the impact on the local environment and receiving waters. Rainwater tanks are typically applied at the household scale for non-potable water source uses such as toilet flushing and garden irrigation. However, this paper reports on a communal approach to rainwater harvesting, where the water is treated for potable use. A communal approach to rainwater harvesting can offer benefits, such as: economies of scale for capital costs, reduced land footprint, centralised disinfection and flexibility in matching supply and demand for different households. The analysis showed that the communal approach could provide a reliable potable water source to a small urban development. However, there was an energy penalty associated with this water source compared to centralised systems that could be addressed through more appropriate pump sizing. The outputs from this monitoring and modelling study demonstrated rainwater harvesting can be expanded beyond the current mainstream practices of household systems for non-potable use in certain development contexts. The analysis contained in this paper can be used for the improved planning and design of communal approaches to rainwater harvesting.     

Investment Evaluation of Rainwater Tanks

Melbourne, Australia faced fourteen consecutive years of below average rainfall before drought breaking rains in 2010. Melbournians are also concerned about the significant increase in potable water price in the future where the cost is expected to increase by 100% in 5 years. Stormwater harvested using rainwater tanks is an alternative source of nonpotable water source where potable quality water is not required for use. However, prior to installing rainwater tanks, customers expected to investigate the financial viability of installing tanks. The objective of this study is to carry out cost effectiveness analysis to estimate the payback period, cost effectiveness ratio and the levelized cost of installing rainwater tanks in different geographical locations with significantly varying mean annual rainfall (MAR). The paper also focuses on the impact of the inflation rate, interest rate (discount rate), the period of analysis on the previously stated cost parameters and determines the optimum tank size based on the MAR of the location. The study showed that the payback period was as low as 14 years for a 5kL tank in an area where the MAR is around 1000 mm (discount rate of 10% and inflation rate of 4.2%). The payback period varied considerably with the tank size especially in low rainfall areas (MAR ≤ 450 mm). This emphasizes the importance of selecting the optimum tank size to ensure maximum use of the rainwater to maximize the return on the initial investment.     

An Optimization Approach for Assessing the Reliability of Rainwater Harvesting

This study was aimed at developing an optimization approach to rainwater harvesting (RWH) considering three (3) water consumption scenarios (WCS). These scenarios which include basic water need (BWN), pour flush (PF) and full plumbing connection (FPC) corresponding to 50 litres per capita per day (lpcd), 75(lpcd) and 150(lpcd) respectively were simulated for different categories of buildings. Reliability of supply was determined by first obtaining composite surplus/deficit of rainwater followed by optimizing the redistribution of surplus rainwater harvested to deficient buildings. Results showed that when total annual rainfall intercepted by roof exceeded total demand, 100% reliability of water supply was guaranteed. Reliability was found to be a linear function of storage. When reliability of supply is possible, the optimized storage bears an inverse exponential relationship to the roof plan area per capita. The relationship between surplus/deficit and roof plan area per capita follows a one-phase decay pattern. An optimal redistribution of surplus water from self-sufficient buildings to deficient ones gave an improvement in supply reliability from 64 to 87% for basic water need, 47 to 58% for pour flush and 28 to 29% for full plumbing connection.     

The effect of selection of time steps and average assumptions on the continuous simulation of rainwater harvesting strategies.

The use of domestic rainwater tanks with back up from mains water supplies in urban areas can produce considerable reductions in mains water demands and stormwater runoff. It is commonplace to analyse the performance of rainwater tanks using continuous simulation with daily time steps and average water use assumptions. This paper compares this simplistic analysis to more detailed analysis that employs 6 minute time steps and climate dependent water demand. The use of daily time steps produced considerable under-estimation of annual rainwater yields that were dependent on tank size, rain depth, seasonal distribution of rainfall, water demand and tank configuration. It is shown that analysis of the performance of rainwater tanks is critically dependent on detailed inputs.     

Rainwater: A Potential Alternative Source for Scarce Safe Drinking and Arsenic Contaminated Water in Bangladesh

Although Bangladesh receives plenty of rainwater during its monsoon, both rural and urban areas suffer from shortages of safe drinking water during dry season. Arsenic contamination of ground water affects many rural areas, whilst some urban areas including the capital, Dhaka City, lack sufficient potable ground water to meet the demand. To cope with the problem, this research explore: the feasibility of harvesting rainwater during monsoon as a source of quality safe drinking water in Dhaka City. A questionnaire survey was conducted about potable water shortage in four slums of Dhaka City. Rainwater was collected using a non-toxic waterproof cloth as a catchment during monsoon and stored in a ferro-cement storage tank with an initial flushing device attached at the inlet of the tank. Different important physical, chemical and bacteriological parameters were tested throughout the storage period of 4 months. The efficiency of the rainwater harvesting system increased from 51% to 80% before and after installing the system. The test results were compared with the Bangladesh water quality standards. The tests have revealed slightly higher pH value (8.1 to 8.3) and enormity of color beyond the acceptable range. Although the presence of total coliform was detected after three months, traditional filtering of that stored rainwater showed a promising solution to mitigate potable water shortages in Bangladesh.     

Identifying the major influences on the microbial composition of roof harvested rainwater and the implications for water quality.

Perceptions of the quality of roof harvested rainwater remain an impediment to widespread implementation of rainwater tanks on urban allotments. Previous literature reports on roof water quality have given little consideration to the relative significance of airborne environmental micro-organisms to roof catchment contamination and the issue of tank water quality. This paper outlines the findings of a recent study into the influence of weather on roof water contamination conducted at an urban housing development in Newcastle, on the east coast of Australia. Samples of direct roof run-off were collected during a number of separate rainfall events, and microbial counts were matched to climatic data corresponding to each of the monitored events. Roof run-off contamination was found to be under the strong influence of both wind speed and direction. The preliminary findings of an investigation currently under way into the microbial diversity of rainwater harvesting systems have also been presented. The results indicate that the composition of organisms present varied considerably from source to source and throughout the collection system. In all cases, evidence of faecal contamination was found to be negligible. The implications of these findings to the issues of tank water quality, health risk analysis and monitoring protocols have been discussed.     

Implications to stormwater management as a result of lot scale rainwater tank systems: a case study in Western Sydney, Australia

Rainwater tanks are increasingly adopted in Australia to reduce potable water demand and are perceived to reduce the volume of stormwater discharge from developments. This paper investigates the water balance of rainwater tanks, in particular the possible impacts these tanks could have in controlling the stormwater discharge volume. The study collected water quantity data from two sites in the Hawkesbury City Council area, New South Wales, Australia and utilised the collected data in a simple water balance model to assess the effectiveness of rainwater tanks in reducing the stormwater discharge volume. The results indicate that a significant reduction in discharge volume from a lot scale development can be achieved if the rainwater tank is connected to multiple end-uses, but is minimal when using irrigation alone. In addition, the commonly used volumetric runoff coefficient of 0.9 was found to over-estimate the runoff from the roof areas and to thereby under-estimate the available volume within the rainwater tanks for retention or detention. Also, sole reliance on the water in the rainwater tanks can make the users aware of their water use pattern and water availability, resulting in significant reductions in water use as the supply dwindles, through self-imposed water restrictions.     

Water Quality Monitoring and Hydraulic Evaluation of a Household Roof Runoff Harvesting System in France

The quality of harvested rainwater used for toilet flushing in a private house in the south-west of France was assessed over a one-year period. Twenty-one physicochemical parameters were screened using standard analytical techniques. The microbiological quality of stored roof runoff was also investigated and total flora at 22°C and 36°C, total coliforms, Escherichia Coli, enteroccocci, Cryptospridium oocysts, Giardia cysts, Legionella species, Legionella pneumophila, Aeromonas, and Pseudomonas aeruginosa were analysed. Chemical and microbiological parameters fluctuated during the course of the study, with the highest levels of microbiological contamination observed in roof runoffs collected during the summer. Overall, the collected rainwater had a relatively good physicochemical quality but variable, and, did not meet the requirements for drinking water and a microbiological contamination of the water was observed. The water balance of a 4-people standard family rainwater harvesting system was also calculated in this case study. The following parameters were calculated: rainfall, toilets flushing demand, mains water, rainwater used and water saving efficiency. The experimental water saving efficiency was calculated as 87%. The collection of rainwater from roofs, its storage and subsequent use for toilet flushing can save 42 m³ of potable water per year for the studied system.     

Preliminary Assessment of Rainwater Harvesting Potential in Nigeria: Focus on Flood Mitigation and Domestic Water Supply

This study was accomplished using 26 locations in the major ecological zones of Nigeria as well as different classes of residential buildings and different levels of water consumption. For each location, house dwelling class and level of water consumption, a water balance approach was used to assess the proportion of water demand that can be met by rainwater. Results obtained indicate that for all the locations in the rainforest zone and some parts in the guinea savanna zone, over eighty percent (80 %) of water demand of those living in bungalows can be met by rainwater. Rainwater harvesting potential was found to be a power function of rainfall coefficient of variation, with coefficient α and exponent β. High correlation coefficients (0.881?≤?R ² ?≤?1) were obtained between coefficient α and roof area per capita. Also, high correlation coefficients (0.847?≤?R ² ?≤?0.992) were obtained between exponent β and roof area per capita.     

用于裂隙岩溶含水层回灌的屋面雨水径流水质特性研究

本文以北方地区裂隙岩溶水典型城市济南市为研究区，监测分析了2008年2月至8月降水过程的降雨量、降雨强度，同时对研究区13次天然降水的11项指标与位于裂隙岩溶水直接补给区7次降水形成的屋面径流的28项指标进行检测，识别出屋面径流主要污染物类型，探讨了2008年春季和夏季各次降雨形成的屋面径流中不同污染物随降雨历时、降雨强度和季节的变化规律；分析了径流污染物的来源，并对屋面径流雨水通过井回灌裂隙岩溶含水层用于饮用水的处理方法及效果进行了探讨。济南市屋面水质的研究为济南城市屋面雨水回灌裂隙岩溶含水层提供了依据。     

初期弃流后板房屋面雨水污染物质量浓度衰减规律

为研究初期雨水弃流后不同降雨重现期条件下屋面雨水的污染物质量浓度变化规律,以板房屋面为例,采用3 mm的初期雨水弃流深度,基于暴雨径流管理模型(SWMM),构建了板房屋面径流模型,在采用雨水收集箱中污染物质量浓度实测值对模型验证后,模拟分析了不同降雨重现期板房屋面雨水的污染物质量浓度衰减规律.结果表明:雨水收集箱中污染...     

Assessing the Potential for Rainwater Harvesting

Rainwater harvesting is one of the promising ways of supplementing the surface and underground scarce water resources in areas where existing water supply system is inadequate to meet demand. Rainwater harvesting is one of the measure for reducing impact of climate change on water supplies. Abeokuta has a mean annual rainfall of 1,156 mm which makes rainwater harvesting ideal. Intra annual variability lies betwen 0.7 and 1.0 while the inter annual variability was 0.2. Annually 74.0 m³ of rainwater can be harvested per household. Estimated annual water demand for flushing, laundry and flushing were 21.6 and 29.4 m³ respectively. Harvested rainwater in Abeokuta can satisfy household monthly water demand for WC flushing and laundry except for November, December, January and February. The excess rainwater stored in September and October is sufficient to supplement the short fall in the dry months provided there is adequate storage.Water savings potential is highest in June and September which is the two rainfall peak period in Southwest Nigeria.     

山地城市屋面雨水可利用量分析——以重庆市沙坪坝某片区为例

为定量评估山地城市屋面雨水可利用量,以重庆市沙坪坝某片区为例,分析了重庆市的降雨特征,利用改进的径流系数法定量评估了代表年屋面雨水可利用量,并分析了降雨特征对可利用量的影响;运用设计降雨量和设计暴雨强度两个指标相结合的方法确定了蓄水池规模,使其满足径流控制率和防洪减涝的要求。研究表明:在代表年降雨量为1 198.9、1 104.4和962.7 mm时,研究区域屋面雨水可利用量分别为267 951.8、247 421.3和198 917.9 m~3,雨水利用潜力较大,降雨量对可利用量的影响较大,而降雨强度对其影响很小;研究区域蓄水池总规模为9 312 m~3,屋面径流控制率达到86.4%,为山地城市雨水利用系统中蓄水池的规模设计提供了参考依据。     

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.     

建筑屋面雨水有压回补地下水理念与潜力评估

城市雨水回补地下水对增加城市地下水资源、减轻内涝灾害具有重大意义。屋面雨水水质较好,且具有高水头特点,并无需外界提供电能、不占据多余空间,可实现雨水收集、快速净化,形成屋面雨水有压回补地下水模式,增加地下水回补率。该技术理念提出后,尚处于研究阶段,故本文以天津大学新校区为研究区,通过水泵加压回补地下水的现场数据推导出了半经验公式,选取与实地状况基本相符的渗透率等相关参数,对该模式进行相关计算与潜力评估。利用天津市暴雨公式计算了不同降雨重现年及历时的设计雨强,并计算出本模式应用于研究区的不同设计情况下的回补率。计算结果显示,回补率与降雨历时(建筑屋面汇水或滞留时间)呈正相关关系;假设建筑屋面雨水滞留时间为24 h时,25年一遇以内降雨回补率大于90%,50年一遇和100年一遇降雨回补率达85%以上。本文论证了该种模式具有很强的应用价值,对雨水回补地下水技术研究有一定的参考价值。     

Ensuring water security by utilizing roof-harvested rainwater and lake water treated with a low-cost integrated adsorption-filtration system

Drinking water is supplied through a centralized water supply system and may not be accessed by communities in rural areas of Malaysia. This study investigated the performance of a low-cost, self-prepared combined activated carbon and sand filtration (CACSF) system for roof-harvested rainwater and lake water for potable use. Activated carbon was self-prepared using locally sourced coconut shell and was activated using commonly available salt rather than a high-tech procedure that requires a chemical reagent. The filtration chamber was comprised of local, readily available sand. The experiments were conducted with varying antecedent dry intervals (ADIs) of up to 15 d and lake water with varying initial chemical oxygen demand (COD) concentration. The CACSF system managed to produce effluents complying with the drinking water standards for the parameters pH, dissolved oxygen (DO), biochemical oxygen demand (BOD₅), COD, total suspended solids (TSS), and ammonia nitrogen (NH₃-N). The CACSF system successfully decreased the population of Escherichia coli (E. coli) in the influents to less than 30 CFU/mL. Samples with a higher population of E. coli (that is, greater than 30 CFU/mL) did not show 100% removal. The system also showed high potential as an alternative for treated drinking water for roof-harvested rainwater and class II lake water.