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Published on: 21/10/2011

Comparing the cost benefits of different water systems is notoriously difficult for reasons ranging from uncertainties about the lifespan of infrastructure, to lack of relevant and specific data, and exchange rate fluctuations.  Mostly, it is difficult because the full costs of systems are rarely documented and, even if they are, they are not set against real world benefits. When people pay for water, what counts for them is the level of service they receive in terms of quality, quantity, reliability and access, rather than the shiny new storage tank. Perhaps, even less is known about the full costs of providing rainwater harvesting (RWH) than for many other systems.

Prepared by IRC and WASHCost, with the support of the Rain Foundation, this report indicates that while the initial capital costs (per capita) of rainwater harvesting (RWH) systems can be relatively high in comparison to systems that do not need storage tanks (e.g. a handpump supplying water to a large number of users).   In contrast, capital costs (per capita) for RWH can be relatively low when compared to the costs of, say a piped water supply system that involves construction of overhead tanks. 

In terms of RWH water storage, typically the capital costs of per m3 of water stored are in the range US$ 40 - 200 when water is stored in jars and tanks, while capital cost per m3 of storage for sand dams is more likely to be in the range US$ 10 - 25. These costs are calculated in US dollars for the base year 2008, converted using purchasing price parity (PPP2008) – allowing for inter-country comparisons without the distorting effects of exchange rates.

Rainwater systems may be relatively robust, but they will require maintenance (operational and maintenance expenditure or OpEx), and after a number of years, major elements will need to be renewed or replaced (capital maintenance costs or CapManEx).  This study highlights the importance of maintenance costs in extending the useful lifespan/s of RWH systems and thereby ensuring a good return on the original investment.  Routine maintenance costs are, in general, relatively low for RWH systems.  However, it should be noted that both routine and capital maintenance costs are both dependent on the quality and repair-ability of the original RWH system.

Direct and indirect support costs will also need to be considered.  Some support costs directed to the community may include promoting rainwater harvesting systems, showing people how to install or improve them, and promoting their hygienic use. Indirect support costs are costs that often take place at a higher level where policy is set, and regulations for safe use, for example, are developed.

These costs describe above are collectively known as the life-cycle costs (LCC). LCC components that are often neglected result in impaired or the rapid decline of system functionality after construction.  As important, just comparing the CapEx of different water supply systems may be misleading.  It is better to compare LCC costs and, more specifically, annualised costs per m3 of water supplied (rather than m3 of water storage capacity) because this takes account of both the system lifespan and level/s of service experienced by users. 

Finally, RWH systems have unique advantages. They allow households to manage their own supply, they support productive uses (e.g. backyard gardening, watering livestock, etc.), and they supply water for drinking and cooking.  They can also provide an excellent back-up supply making communities more resilient when primary systems fail.  They also are especially useful in areas where ground water is scarce or polluted.  However, making rainwater harvesting systems sound cheaper than they are, does not do the technology or the movement behind it any favours.  Emphasis should be placed on demonstrating that rainwater harvesting provides value for money in terms of resilience, flexibility and level of service that is provided to users.

21 October 2011. 



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