Evaluation of rainwater harvesting in Portugal: Application to single-family residences
Introduction
The goal of reducing by half the proportion of people without sustainable access to safe drinking water until 2015 set in 2000 by UN Millennium Development Goals is far from being fulfilled in some parts of the globe (UN, 2013). Currently, it is estimated that roughly one billion people do not have access to safe drinking water (Helmreich and Horn, 2009). This is more critical in developing countries, particularly in poor rural areas, where at least one-third of the population has little or no access to safe drinking water and results in major health problems from waterborne diseases (WHO, 2002; UN, 2013). In addition, several parts of the globe already face water scarcity, most notably in Africa, and it is estimated that by 2025 two thirds of the world's population will face water related challenges (UNEP, 2002). Therefore, water is a key at-risk resource and improved water management of it is essential since resource optimization benefits the economy, environment and society (UN-HABITAT, 2005, White et al., 2007).
In Europe, generally, the risk of water scarcity is smaller. However, providing public water supply consumes a significant amount of other resources, e.g., building, maintaining, operating and rehabilitating/replacing the supporting infrastructures (USDE, 2006, Arpke and Hutzler, 2006). Consequently, even in countries with a favorable balance between water demand and water availability, there is interest in evaluating alternatives for improving the efficient use of water. Therefore, organizations with responsibilities in the water sector have been motivated to promote a more efficient water use. In developed nations, there has been a stabilization or reduction of the water use in various sectors (e.g., residential; industry; agriculture) due to the combined implementation of structural (e.g., reduction of water losses) and non-structural (e.g., education campaigns) measures (Dworak et al., 2007).
In order to optimize water management, two main categories of solutions can be identified: (i) reduction of water consumption; and (ii) identification of new water sources. The former includes solutions that promote changing consumption habits and the adoption of lower consumption devices, such as low-flush toilets. The latter includes exploring alternative sources for public water supply. For buildings in general, and residential buildings in particular, one of the most common alternative sources is the rainwater – the scope of the present paper. This reviews the most relevant technical and economical issues in designing domestic rainwater harvesting systems, evaluating the technical and economical feasibility of implementing this technology in Portugal. The evaluation is performed for single-family residences from data gathered by Carvalho (2011).
Section snippets
General context of rainwater harvesting
Rainwater harvesting (RWH) comprises the collection, storage, treatment and use of rainwater as either a principal or supplementary source of water. This water source has been used for thousands of years throughout the world for both potable and non-potable applications (Fewkes, 2006). In developing countries such as Bangladesh, Botswana, China, India, Kenya, Mali, Malawi or Thailand (UN-HABITAT, 2005, TRCA, 2010), RWH is being used mostly to cope with water shortages for potable and
Methodology
One way to evaluate the economical viability of the installation of a RWH system is to estimate the time period required to recover the project investment. In order to be competitive, a return on investment is expected within a reasonable period of time, the so-called payback period. The lower the payback period, the more interesting the investment becomes. The limit when an investment is no longer attractive depends on several factors. For buildings, it is common to use a 50 year timescale,
Discussion of results
The methodology described in the previous section was applied to a single-family house consistent of 2 bedrooms, 1 living room, 1 bathroom and 1 kitchen. Next to the house there is a detached single car garage. The roof view is schematically presented in Fig. 9 and three collection areas were considered: A – 78.6 m2; B – 103.4 m2; and C – 131.4 m2.
The RWH efficiency, defined as the ratio between the harvested rainwater and the available rainwater is presented in Fig. 10 for the different
Conclusions and future developments
The results of the economical viability analysis performed should be considered conservative, i.e., the projected payback periods may be shorter than predicted. Directly related to water supply, RWH has the potential for reducing resources consumption in providing water supply that were not considered (e.g., IPCC, 2007, Fowler et al., 2007 refer to the reduction of greenhouse gas emissions from water storage reservoirs and water treatment processes which contribute to climate change). However,
Acknowledgements
The authors acknowledge ICIST-IST Research Institute. The authors would like to thank the anonymous reviewers for their valuable constructive comments and suggestions that improved the manuscript significantly.
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