As a part of the family of green technologies, RWH can be defined as the capturing of rain runoff from roofs and other surfaces and storing it for a later purpose (Despins et al., 2009). As an ancient practice, RWH cisterns were common in ancient Greek, Etruscan, Roman, Indian, and other civilizations (Boers and Asher, 1982). In Jordan for example, surface runoff has been collected for over 4000 years. Elsewhere, archaeological research in Venice resulted in the identification of more than 6000 subterranean rainwater cisterns constructed during the Middle Ages for domestic water supply. More recently, the advent of urban sprawl has resulted in a decrease in the amount of forested lands, wetlands, and other forms of open spaces that absorb and clean storm water in the natural system (Leopold, 1968). This has caused degradation in the water quality of water bodies that are now used in the agricultural and domestic sectors. The practice of RWH has been gaining popularity as the usage of rainwater is much cleaner (in terms of carbon dioxide emissions) than the usage of municipal water supplies. Like other water conservation techniques, RWH is considered to be a viable means to manage urban water resources more efficiently and sustainably (Basinger et al., 2010).
Domestic water usage is a significant component of the global water demand. RWH can be used for both nonpotable and potable purposes such as garden use, toilet flushing, washing clothes, hot water systems, and drinking water supply (Khastagir and Jayasuriya, 2010). Catchment area, storage material, and the distribution system are a few design considerations that have to be taken into account when constructing a RWH system. When selecting a rainwater tank, a house owner often only focuses on the location where the tank will be placed, its aesthetics, and the cost. However, other key design variables that need to be considered are: amount of precipitation in the area, extent of catchment area, and the end use of the water. If the tank is sized properly, the volume of rainwater in the tank will be able to supplement the household water demand; this also reduces the chances of the tank being empty or overflowing. Also, if the catchment area is fairly large, a greater number of end-use applications can allow for greater water savings.
According to the United Nations Environment Programme (UNEP, 2012), examples of RWH and its utilization can be found all across the world. For example, with almost 86% of Singapore’s population living in high-rise buildings, using RWH has become an important component of reducing rising urban water demand in the region. In cities and regions such as Tokyo, Thailand, and China, RWH is seen as a way of mitigating water shortages, controlling floods, and securing water for emergencies. In Bangladesh, where the rural population is plagued by arsenic in the drinking water, RWH is being used to provide a potable water supply, and in St. Thomas, U.S. Virgin Islands it is now mandatory to install a RWH system to acquire a residential building permit.
In Canada, a study in Ontario by Farahbakhsh et al. (2009) indicated that if there are no weather anomalies and the precipitation pattern follows the historical trend, then municipal water demand can be reduced by as much as 47% in domestic households in Ontario, Canada, if RWH is used for domestic water supply. In southeast Brazil, Ghisi (2006) estimated that RWH practices can reduce potable water demand by 48% to 100%. In Germany, where RWH has been in use since the 1980s, potable water demand has decreased by 30% to 60% due to the use of roof runoff harvested in 4- to 6-m3 tanks, which is then used for toilet flushing (Hermann and Schmida, 1999). RWH is being used in the rural areas of the developing world (such as India, China, and Africa), where it is mainly used for irrigation during dry periods. In such environments, RWH is seen as a measure that can help fight food scarcity (Fox et al., 2005).
The quality of water collected in a RWH system is affected by several factors, which include the proximity to roads and heavy industries, presence of wildlife, and meteorological conditions such as temperature and rainfall patterns in the region (Despins et al., 2009). Although these factors may deteriorate the quality of the collected rainwater, Kumar (2004) states that treatment by prestorage treatment devices such as filtration or first flush diversion can help to expel most of the harmful sediments from the roof (catchment area) into the surroundings and also prevent the stagnation of water in the tanks, thereby restricting the breeding of insects. Similarly, poststorage treatment devices such as ultraviolet disinfection, chlorination, or slow sand filtration can further improve the water quality, in some cases making the harvested rainwater a source of potable water. As an added precaution, storage tanks must be closed at all times to prevent the entry of insects and to reduce evaporation losses. Finally, the most commonly occurring problem of algal blooms in storage tanks can be mitigated by both chemical and physical techniques (Bartsch, 1954). Chemical techniques include the use of copper sulfate in small concentrations such that the algal bloom is destroyed without harming the roots of the plants (if the water is used for irrigation). Even though the solution is effective, it is not viable as the cost of implementation rises with increasing volumes of water in the storage tank. Covering the storage tanks with a reflective material, which prevents sunlight transmission into the water tanks, is an alternative solution (Bartsch, 1954). This is a significantly less expensive and more practical approach. Another issue that must be addressed in the design of RWH systems is the handling of overflows during large rainfall events. Methods for handling overflow may include onsite infiltration, as well as discharging to an existing storm sewer infrastructure (Farahbakhsh et al., 2009).
The cost of a RWH system varies depending on the size of the catchment area, the type of cisterns chosen to store the rainwater, and the piping material used to transport the water for its end use. Cost was by far the biggest barrier identified for the implementation of RWH systems in a recent study conducted by Farahbakhsh et al. (2009); the typical roof area of a domestic household in Canada is ≈230 m2 (Canadian Mortgage and Housing Corp., 2012), which translates to a cost in the range of C$2000 to C$8000 (in Canadian dollars) or the setup of a RWH system. The yearly maintenance costs and decommissioning cost at the end of the lifespan of the systems costs an additional C$2000 (Roebuck and Ashley, 2006). It should be noted that RWH systems have one of the lowest payback periods for sustainable engineering systems (maximum 15 years), and government incentives can often offset some of the expenses (Despins et al., 2009).
The Faculty of Agricultural and Environmental Sciences on the Macdonald Campus of McGill University has been active in the promotion of sustainable technologies. The Horticulture Research Center at the Macdonald Campus serves as a training, education, and research center for students involved in vegetable and fruit production and is used by numerous departments on the campus. The Horticulture Services Building is used as a storage, processing, and retail space for the activities that occur in the surrounding gardens and the two greenhouses. Irrigation of the greenhouses consumes ≈700 gal of freshwater per day. The objective of the RWH project described in this article is to manage urban water resources more efficiently and promote the learning of practical sustainable technologies at the university and the surrounding communities through educational tours to the project site. Although research on domestic RWH systems has been increasing, there are still relatively few publications that describe the construction and advantages of such systems. This article is intended to fill this gap by explaining cost-effective ways for the setup and maintenance of this sustainable water supply option.
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