Harvesting Rainwater from Buildings

Water is life and a primary need of all living beings. Human beings also need water not only for survival but also for their multipurpose and ever increasing needs other than the basics. The amount of usable water on the Earth’s surface is continuously shrinking and becoming polluted due to various human activities in the name of development. When surface waters, as a primary choice, are being polluted daily, then underground water as a secondary option is continually being extracted in many parts of the globe while the negative impacts of this practice are ignored. In this context, a third option is investigated herein. Buildings of various occupancies are the only infrastructures in which human beings live or conduct various businesses safely and comfortably. For safe and comfortable living in buildings, even for a little while, there is need of water. Providing wholesome water in buildings is therefore a major concern in building development. For buildings, water is generally drawn from a public main running by the side of the building; in unavoidable cases, an independent water source, such as tube well, is used for withdrawing underground water. In many parts of the globe, both surface and groundwater is continually becoming limited due to natural calamities and manmade interventions; in contrast, the demand for building development is increasing with the increase in population and the quest for socioeconomic development. The development of buildings is therefore creating an increase in water demand, which cannot be met by the usual practices depending on the sources of conventional surface and groundwater. Against this backdrop, a third option is envisaged for managing the shortage of water for any building: The practice of rainwater harvesting has been found to be reliable where sufficient rainfall occurs and adequate catchment is available to collect rainwater. In this chapter, the circumstances invoking rainwater harvesting in buildings is discussed, and its history of practice—as well as the present scenario in the global perspective—are delineated. An introduction to buildings and the prospects and the constraints of using rainwater in buildings is also described.

To deal with rainwater harvesting, knowledge of rain, rainfall, and rainwater is necessary. Knowledge of the formation of rain in clouds and its pattern of falling to the Earth’s surface helps one to understand more about quality of rain and the quantity of rain that can be collected for harvesting. To collect rainwater at a particular place, the intensity of rainfall to be measured should be known. A rain gauge is used for this purpose. Installation of a rain gauge and the technique of measuring rain is important. In a particular place, the rainfall pattern and its distribution over a period of time is variable. Therefore, rainfall intensity should be studied and recorded for the planning and design of a rainwater-harvesting system. The nature and quality of the rain, and also of the rainwater, also varies from place to place due to pollution of the air in these areas. As a result, for any place where rainwater harvesting is to be performed, the quality of rainwater must be tested or be known from secondary sources. With a view to enriching the concept of rainwater harvesting in buildings, details about the formation of rain, pattern of rainfall, rainfall intensity, global rainfall scenario, and causes of degrading quality and nature of rainwater are discussed in this chapter.

Rainwater harvesting in buildings involves technology for its proper planning, design, installation, operation, and maintenance. Two major scopes of rainwater harvesting are (1) the use of rainwater for all general purposes and (2) recharging groundwater. In both cases, various functional techniques must be applied. The extent of technological involvement depends primarily on the introduction of various conditioning or treatment technologies in the harvesting system: sedimentation, filtration, and disinfection. Based on the application of these conditioning or treatment technologies, the rainwater-harvesting system in buildings may be classified as (1) a direct-use system, (2) a nonfiltered system, (3) a filtered system, and (4) a complete system. The development process of a rainwater-harvesting system in buildings has four aspects: (1) planning, (2) design, (3) construction, and (4) maintenance. In all aspects of rainwater harvesting‒system development, systematic approaches must be followed to ensure its sustainability. In this chapter, the major scopes of rainwater harvesting are introduced. The extent of technological involvement in the harvesting system is delineated. All aspects of rainwater-harvesting development in buildings and their systematical approaches are discussed. Finally, the problems and prospects of rainwater harvesting in buildings are identified.

A building in use may require water either related to the purpose of the building or for the user of the building. In addition, water is also required to keep the building usable. The use of water in a building may be for a single unique purpose or multiple purposes. To harvest rainwater in a building, it is of the utmost necessity to identify all of the purposes for the use of water and then to estimate the water requirement for those purposes. Water use in a building is mostly a continuous phenomenon throughout the day, and in some cases it is periodical or in few cases occasional. Considering the usual pattern and major purposes for water to be used in a building, the daily water requirement for the purposes of using water in a building should be determined. Water requirement for particular purposes varies depending on multiple factors such as behavioral, economical, social, cultural, environmental, and probable hazards. Therefore, the water requirement for a particular single purpose is not identical or unique for buildings of various occupancy types at various locations. Water requirement, and thus the demand for water for a particular purpose, varies from person to person, from time to time, and from place to place. As a result, the water requirement in a building for a particular purpose and occupancy type varies considerably for various locations. In this chapter, various water requirements for persons and thus for buildings are mostly identified and mentioned in tabular forms. In most cases, the water requirement or demand is furnished on a daily basis. In a few cases, the requirement is given in the context of particular considerations. The water requirement for some purposes, in particular areas on the globe, is also furnished.

To harvest rainwater in building, it is collected from the potential catchments of the building and its surrounding premises. The roof of a building serves as the most effective catchment, but in critical cases various other type of catchments are used. A collection system should be provided to collect rainwater from the catchments. Although roofs are mostly a flat and horizontal surface, roofs of various configurations and inclinations are also seen. As a result, the types of collection and collecting systems, due to roofs of varied shapes, configurations, and inclinations, also differ. The roofs of buildings are mostly made of reinforced cement concrete, but roofs of various other materials also exist. Roofing materials influence the quality of the collected rainwater. Various surface-finishing materials are sometimes used on roofs for various purposes, which also contribute to the quality of rainwater. After a considerable dry spell, the rainwater of the first rain is generally found to be comparatively more contaminated and polluted. Therefore, a considerable amount of such first rainwater must be flushed out. In this chapter, various catchments of buildings, particularly roofs of various designs and materials, as well as the collection approaches and first rainwater‒flushing methodologies, are discussed. Determining size of the rainwater-collecting elements, the volume of rainwater to be collected, and the quality aspects of the rainwater, is also discussed. Finally, ways of maximizing rainwater collection are suggested.

Rainfall is not a continuous phenomenon. Therefore, to make rainwater available when there is no rain and there is dearth of water, rainwater must be collected and stored. A rainwater storage tank is one of the vital elements of rainwater harvesting in a building. Both the quantitative and qualitative aspects of rainwater harvesting are primarily dependent on the storage of rainwater. In developing appropriate and effective storage of rainwater, various factors, such as location, planning, size, aesthetics, and functionality of storage tanks, should be considered. The location of a rainwater-storage tank in a building must be judiciously decided due to having both the advantages and disadvantages of one particular choice out of multiple choices of locating the tank within or outside the building. It is important to plan how the rainwater will be stored, in conjunction with the water collected from other sources subject to the purpose of use considering the quality and quantity of water from different sources. The size of the storage tank is another factor to be decided giving the importance of the demand for rainwater, availability of rainwater, space for storage, and, above all cost of the tank. When tanks should be placed exposed, aesthetics may become a governing factor in deciding the shape and material of the tank. The functionality of the tank can be addressed by the reliability of the quality of stored rainwater. In this chapter, all aspects of rainwater storage are discussed focusing predominantly on the various options for locating the storage tank and identifying the advantages and disadvantages of all of the options.

Rainwater is pure when formed in the cloud, but it becomes contaminated or characteristically changed while falling and flowing over any surface due to absorbing various suspended elements present in the air, and the dirt or chemicals present on the surfaces, coming into contact with the rain or rainwater. As a result, it is rarely possible to obtain pure rainwater for direct consumption, particularly water that is collected in buildings of urban areas. Storing rainwater for a long period might cause further contamination due to the growth of various microorganisms in the reservoir. Therefore, after collecting and storing it, it is necessary to purify contaminated rainwater according to the purpose of use. There are various methods of purifying or conditioning water and thus rainwater. In buildings, considering the qualitative and quantitative aspects of water demand, limited methods of treatment and conditioning systems are generally employed in rainwater harvesting. The treatment methodologies generally adopted are screening, sedimentation, filtration, and disinfection. In this chapter, the usually practiced treatment process recommended for different purposes of uses of rainwater in buildings, are discussed. At the end of the chapter, the planning aspects of treatment systems are delineated.

Buildings are infrastructures that can be built in varying shapes and sizes starting from a single-story cubical to multistory high-rise tubular form. Harvested rainwater may be required to be distributed at various locations of a building in conjunction with the distribution system of water from other sources including independent ones. Like normal building water-supply system, a building rainwater-supply system can also be developed according to one of the two common methods: an underground-overhead tank system or a pressurized direct-pumping system. In designing the pumping and piping system, the same hydraulic principles are followed for both a normal and a rainwater-supply system. In this chapter, two methods of creating a water-supply system are discussed, and the design approaches for the elements used in the supply system are described. Finally some safety measures for preventing contamination of water in the supply system are discussed.

Where there is scarcity of water, it is understood that the dependability on surface water has almost been lost and that the availability of groundwater is either becoming very limited or costly. In such situation where there is potentiality of rainwater harvesting due to having substantial rainfall, there might be sufficient rainwater for using it for some purposes in building projects other than general purpose of uses of rainwater. Improving the groundwater situation using rainwater is considered to be the most effective way of using rainwater other than the use of rainwater for general purposes. Groundwater recharging is the process by which the prevailing groundwater situation is improved in terms of quantity and quality. Rainwater collecting from various catchments of a building can also be effectively used for recharging groundwater through facilitating its percolation into the ground around the building. There are various ways of recharging groundwater using rainwater. Utmost care is taken so that the groundwater is not contaminated through the process of recharging. In this chapter, the soil parameters influencing groundwater recharging and the various ways of recharging are described elaborately. The precautionary measures to be addressed while recharging are pointed out. Finally, the probable impacts of groundwater recharging around buildings by using rainwater, both positive and negative, are also mentioned herein.

It is rare that the available rainwater can be harvested fully either for all purpose of use or for groundwater recharging. Therefore, in the majority of cases there would be need for draining of excess rainwater after needful harvesting. Furthermore, provision for rainwater drainage should be incorporated in all types of rainwater-harvesting systems either for overflowing or disposing of rainwater during certain maintenance or repair works. There are various ways of draining rainwater or stormwater. Among the drainage methodologies, a gravity-drainage system is mostly planned around a building or in a building complex. Therefore, gravity drainage by surface and underground piped drains is discussed herein. Among all of the aspects of drainage, the design of drainage system is emphasized in this chapter. Furthermore, the appurtenances of drainage piping are also delineated.

Rainwater harvesting in buildings involves various items and works of multidisciplinary technology and materials. It may not be possible to acquire multidisciplinary technological knowledge by every professional or decision maker involved in rainwater harvesting. Therefore, for professionals and other practitioners engaged in rainwater harvesting in buildings, knowledge about various items of different technologies is essential for their effective and efficient utilization. It may not be possible to acquire in-depth knowledge of all of the types of elements used; however, some basic concepts are essential.