Executive summary of the occasional paper on "Life-cycle costs of rainwaterharvesting systems" by WASHCost, IRC and the Rainwater Harvesting Implementation Network.
Published on: 25/10/2011
Rainwater harvesting (RWH) is a centuries old technology that has the potential to play an increasingly important role in improving and sustaining water services delivery in many parts of the world. In the study reported here, the comparative utility and benefits of RWH are assessed from a life-cycle costs (LCC) perspective. In the context of water services delivery, life-cycle costs relate to the expenditure that is needed to ensure that water supply systems deliver sustainable and equitable services, throughout its life-cycle, from planning to implementation, operation, maintenance and replacement. In addition, the study looks into historical trends and drivers of RWH adoption, and the life-cycle costs of RWH systems compared to life-cycle costs of other water supply systems.
Comparing the costs and cost benefits of different water delivery systems is notoriously difficult because of the combined influence of factors that include: exchange rate fluctuations; inflation, purchasing power variations; levels of integrity; and, so on. The picture is complicated further by regional and local differences in: service levels; economies of scale; water scarcity, user preferences; and, quality of components (and in relation to lifespan). Given the above, the methodology used in this study centred on identifying and using data that were broadly comparable and, in some cases, could be used to relate costs to service levels (and/or other benefits).
With a few notable exceptions, existing available cost data for RWH and other water supply systems are limited to hardware costs of constructing water delivery systems. Data on software costs related to system design, capacity building, institutional development, establishment of micro-credit systems and so on are difficult to find. It was even more difficult to obtain the data needed to calculate the annualised costs (e.g. lifespan of system components) or, in the case of RWH systems, to estimate the water provided by the systems (e.g. catchment area, rainfall probability, extraction rates during the rainy season). Additionally, limited data was found on capital maintenance (i.e. asset renewal costs) and on direct or indirect support costs, making it impossible to reflect the ideal life-cycle costs that may guarantee sustainability in the analysis. In consequence, a full LCC analysis and comparison of water supply system costs in relation to services provided was not possible. This report therefore recommends for LCC and associated data be documented and shared by organisations involved in promoting and implementing RWH systems.
Notwithstanding the caveats listed above, analysis of information on capital expenditure (CapEx) produced findings that include:
As a generalisation, recurrent operation and maintenance expenditure (OpEx) of RWH systems is relatively low when compared to boreholes and piped water supply systems. OpEx is also low when compared to CapEx. However when annualised CapEx is considered, OpEx is typically in the range of 0-20% of annualised CapEx.
The RAIN Foundation estimates that total post-construction support costs amount to around 10% of total costs. Intuitively this seems appropriate but clearly this percentage will increase to cover work in remote areas as a result of travel costs and increased staff inputs owing to, for example, added time spent for travelling.
Historically water service delivery was viewed as an engineering challenge. It was implicitly assumed was that a supply system comprising of a safe water source and appropriate infrastructure would result in improved services. Although this simplistic assumption has become increasingly discredited, governments and international agencies continue to spend vast amounts of money on installing water supply infrastructure. The results in terms of sustainable and equitable services are, in most cases, as predictable as they are disappointing. The simple fact is that good engineering is an important component of a water supply system but the sustainable and equitable provision of services will only be achieved by ensuring that attention and adequate finance is given to the software component of a supply system. Additionally slippage (or slip back) in service levels will only be avoided or managed by ensuring that funds are available for timely capital maintenance (or asset renewal).
A recent worldwide review of user preference found that the popularity of RWH depended to a great extent on the availability of a public piped water supply system. Because of its convenience, consumers with access to piped water were less inclined to install RWH systems. One caveat, however, was the occurrence or expectation of a crisis. For locations experiencing a water crisis, it was observed that governments were more inclined to promote or mandate RWH installation. Consumers on the other hand were more inclined to invest in the technology. Additionally, a tradition of rainwater harvesting increased the likelihood of adoption of modern RWH systems or technologies.
Whilst they are not a panacea, RWH systems enable household and communities to manage their own water, thereby reducing reliance on public supply systems which may be unreliable or difficult to access. Arguably in areas of increasing water scarcity, household RWH systems provide a more resilient and cost-efficient means of improving household water security than constructing ever more complex and expensive public water supply systems. If the policy is to improve water security by providing users with more than one source (as is the case of India), RWH systems are likely to provide a more flexible and resilient supply than bulk transfer schemes that are fed from surface and groundwater resources that are, in many cases, already over-allocated.
Clearly RWH will continue to provide an attractive and cost-effective means of water supply in areas that have ground or surface water quality problems (e.g. as a result of pollution or natural contaminants such as fluoride or arsenic). Similarly, RWH systems can continue to play a cost-effective role in the development of multiple use water services (MUS) that ensure access to sufficient water for small-scale productive uses (e.g. livestock, horticulture, backyard gardening and other small-scale enterprises).
This study also found water scarcity an increasingly serious problem, even in areas that are relatively well-endowed with water resources. Household RWH could and should be promoted as a mainstream option for improving water security and, as such, it should be financed by a combination of public and private expenditure. This said, some attention needs to be given to the findings from user preference studies. At one level, to find practical solutions to real issues identified by users (e.g. poor taste, water quality that does not meet national standards) and at another, to make modern RWH aspirational in many developing countries in the same way that it has become aspirational (and trendy) to use RWH in many developed countries. Additionally, RWH is rarely integrated into water management strategies as these usually focus exclusively on surface water and groundwater. Countries could and should integrate rainwater harvesting more fully into their IWRM strategies and water security plans.
Many of the threats to sustainable and equitable water service delivery are outside the control of the water sector. These include: climate change, increasing energy costs, economic downturns, population increase and civil unrest. Some of these threats are immediate and predictable (e.g. population increase), whilst others are uncertain in terms of severity, precise nature and timing (e.g. climate change). There are also threats that are completely unforseeable and highly improbable, but may have major impacts.
In response to these potential unknowns, RWH can play a significant role in improving the resilience of water supply systems relative to each of these threats. For example, household RWH systems (e.g. roof water harvesting) are an obvious option for funding under climate-change “no or low regrets” expenditure programmes. With respect to energy costs and reliance on fossil fuels, RWH systems can be designed to operate entirely under gravity. As such, RWH could play an increasingly important role as energy costs increase and as pumped water supply systems become more expensive. With respect to economic downturns, RWH systems may also pose as good options when public finance is in short supply as these systems may be funded in part or wholly by individual households. As far as civil unrest is concerned, since public water supply systems are heavily reliant on timely public expenditure and functional government and/or community-based institutions, these are more susceptible to civil unrest, compared to household RWH.
Successful RWH systems require software support that include: cash or a source of finance; knowledge, capacity and/or skills for designing, constructing and operating a system; access, entitlements or tenure over a catchment area; a user group of some kind in the case of communal RWH systems and, the time and/or inclination to construct and operate a RWH system. These software requirements can be a major constraint for the poor or marginalised. It is important, therefore, that any RWH programme takes a pro-poor strategy that helps the poor and marginalised overcome software constraints. If doing so is not feasible, steps will need to be taken to ensure that excluded groups have access to alternative water supply systems.
Intensive use of RWH systems, especially when coupled with increased groundwater extraction for irrigation, can and do impact on downstream water availability. Safeguards should be put in place to ensure that intensification of upstream water use does not impact on the primary needs of downstream users and/or the functioning of important aquatic eco-systems.
In conclusion, this study has highlights a number of important issues:
