The use of water in buildings has an indirect but large contribution to energy and resource consumption. The production and distribution of water for buildings is an energy-intensive activity. Energy is used to purify fresh water sources to a level that is safe for consumption in buildings and to run pumps for cleansing and distribution. In many regions where fresh water is a scarce resource, additional energy is required to extract water from deep underground, to transport water from a long distance, or to operate an energy-intensive desalination plant, etc. Furthermore, transferring wastewater back to the treatment plant requires energy for pumping. At the wastewater treatment plant, electricity is required for wastewater aeration and other treatment systems. It is estimated that 30-40% of the electricity used by mid-sized cities is used to pump water through the distribution system and treat wastewater (Johnson Controls, 2011). Therefore, if we conserve water, we conserve energy.
In brief, water efficiency in buildings has a strong link to energy saving and climate change mitigation. Therefore, water efficiency technologies are discussed on ClimateTechWiki as a mitigation option in the building sector.
This article is about water efficiency in buildings. ClimateTechWiki also has a specific article on 'Water-efficient fixtures and appliances'.
Four key water efficiency technologies for buildings are discussed in this section: metering and water consumption information, rainwater harvesting systems, grey water re-use systems, hydro-pneumatic water supply systems, and water-saving devices.
Metering and water consumption information is one of the key technologies to help manage water consumption. Conventionally, water consumption information is only provided in a form of monthly water bills without much detail in water consumption. Moreover, in many cases, users do not have access to such information, such as in commercial buildings or in multi-dwelling building complexes, where many units share one common water meter. Separate metering and provision of detailed water consumption information helps users to monitor the amount of water consumed and their consumption patterns. They help users to become more conscious in their daily water consumption and catalyse water saving behaviours.
Rainwater harvesting systems facilitate collecting good quality water from natural precipitation. The most popular method of harvesting rainwater is collection from roofs or other building surfaces. A simple system includes roof gutter and downspouts, which run into a storage tank. A detachable downspout is often used to exclude the first runoff during a rainstorm. The first runoff is usually contaminated with dust, leaves, insects or bird droppings.
An advanced rainwater harvesting system includes a water treatment system (e.g., solar distillation), so that the harvested water can be treated to a potable level. An example of innovative rainwater harvesting application in multi-storey buildings places the rainwater storage immediately under the roof to take advantage of gravity for landscaping irrigation, toilet flushing, and other non-potable water usages.
See also the specific article on 'Rainwater harvesting'.
Grey water reuse systems recycle and reuse grey water from shower/bath drain, basins and sinks for non-potable water uses, such as toilet flushing and irrigation, within a building. A grey water reuse system often consists of a piping network to channel grey water from its sources to a treatment system (e.g., sand filter and filtering planter), a holding tank, and distribution pipe to end use points, such as the irrigation system.
Hydro-pneumatic water supply systems introduce air pressure into water tanks as a key energy-saving component in water supply systems for building use. The compressed air in the tank serves three main functions;
- Supplying water at a preset pressure range
- Reducing pressure surges in the water supply systems
- Using the pressure setting to monitor and control water pumps. Energy saving is achieved through reduced energy consumption from water pumps.
Water-saving devices: Four types of water saving device have been developed to save water consumption in buildings. First type of products applies aeration technology which mixes air to the water flow to reduce the amount of water released. This type of device acts as a water flow regulator and can be as simple as a thimble that can be fixed onto almost any domestic water tap, such as those at kitchen sinks and hand wash basins. Kitchen sink taps fixed with flow regulator can achieve a flow rate of less than 6 litres per minute without compromising the water pressure. Compared to the 15 litres per minute flow rate in typical kitchen water taps without regulators, the devices reduce water consumption by more than 60%. Aeration technology has also been applied to showerheads to achieve a flow rate of less than 5 litres per minute.
The second type improves the design of toilets and urinals to reduce the amount of water released, while maximising the cleaning effect. For example, a water efficient urinal with a standard 300mm width only requires less than 0.5 litres of water per flush. For toilets, dual flushing cisterns have been developed to accommodate different flushing requirements. The recommended capacity is 4.5 litres or less for a full flush, and less than 3 litres for a half flush (BCA, 2007).
The third type relates to water saving appliances, such as dishwashers and clothes washers. Technology development and new designs have resulted in significant water savings for these devices. For example, water saving dishwashers use about 14-38 litres of water, compared to the conventional ones that use 34-45 litres of water per load of dishes. The new design approach of clothes washers has moved away from top-loading models to front-end loading ones that use a tumbling action to wash clothes. Front-end loading washers use 30-50% less water, as well as 50-60% less energy to operate, compared to toploading washers.
The fourth type relates to the design and application of automation technologies in landscape irrigation systems. For example, water saving drip irrigation systems use 30%-50% less water than sprinkler irrigation systems. Drip irrigation systems supply water directly to the roots of plants at a slow speed. As a result, water run-off and evaporation rates are kept to a minimum (BCA, 2007). Advanced water saving irrigation technologies also include automated controls that can be used with rain sensors. Irrigation is stopped when rain is detected. An automatic drip water irrigation system with rain sensors and timer controls in tropical regions can save 23% of the annual water consumption in a large building complex (BCA, 2007).
Metering and water consumption information. In single dwelling units or small-scale single-owner buildings, water meters can be installed at the entrance point where the building’s water supply pipe is connected to the municipal water supply pipe. A simple, small space should be provided to protect the meter from weather. The water meter, however, should be easily accessible for reading. It is usually located next to the entrance gates or front doors of buildings. In more complex buildings, which include several major water-consuming systems, i.e., hot water devices, landscaping irrigation and cooling towers, submeters can be installed for each of these systems. Data from all the sub-meters can be linked to the central building management system and provided to end users (where applicable) to optimise water usage and ease of leak detection.
Rainwater harvesting systems can be most easily applied in single dwelling units or townhouses, where homeowners can collect rainwater for their own consumption. In multi-storey buildings with multipleowners, the harvested rainwater is best used for common areas that have non-potable water needs – i.e., landscape irrigation or cleaning of common areas. Rainwater collected from a roof should not be used for potable purposes without proper treatment. The size of a storage tank is based on the roof catchment area and local rainfall data, such as rainfall intensity, frequency and duration. Gutters and downpipes should be made of non-corroding materials, e.g., PVC, galvanised iron, etc., for durability and hygiene reasons. Rainwater harvesting systems require regular clean up of contaminants, dry leaves, etc., which could clog the system and pollute the collected water.
Grey water reuse systems. Conventionally, grey water and black water share the same piping network in a building. Black water is wastewater loaded with biological materials, discharged mainly from toilets. Grey water re-use systems require early attention at the building design stage, as the systems need spaces for additional piping networks, which is separate from the sewer, or the piping network for black water. In addition, treatment systems and holding tanks also require additional spaces. The stored grey water should be used as soon as possible. Preventive measures should be in place to disinfect the stored water to prevent cross contamination and the growing of bacteria and fungus. If the treated grey water is not disinfected, it is recommended to be reused only for irrigation via a subsurface system. Only when grey water is disinfected and treated to meet certain quality standards, can it be used for toilet flushing and surface irrigation (Government of Western Australia, 2010). Grey water re-use systems require regular maintenance to check for potential leaks, replace treatment medium, and to prevent mosquito breeding and bacteria growth.
Hydro-pneumatic water supply systems require space for the air-pressured water tank. It is usually placed on the roof of a building. The space should be large enough for the tank and for maintenance access. The roof and the supporting structure should be able to take in the additional load of the tank plus the designed maximum water capacity. Sensors are required to monitor the water level and pressure. The sensors send signals to control the operation of the compressor and water pump. It is best to link the whole system to the central building management system (if available) for centralised monitoring.
Water-saving devices: can be easily applied in both new and existing buildings. Devices, such as aerators or flow regulators, can be simply added onto existing water taps. Dual flush low capacity flushing cisterns and water efficient urinals can be installed in new buildings or specified to replace existing conventional devices. There are no additional maintenance requirements compared to conventional devices.
Water efficient irrigation systems. The irrigation frequency needs to be programmed to fit the weather and seasonal requirements. It is also recommended to identify opportunities for zone control, so that plants with different types of water needs are irrigated separately. Automatic controls can then be programmed to turn on/off the irrigation systems for different zones to meet various water needs. This arrangement will cut down unnecessary over watering.
Feasibility for implementation
Feasibility for implementation of water efficiency technologies and practices is usually contextually-based. In a rural setting where the communal water supply is limited or not available, rain water harvesting systems and grey water reuse systems are most suitable, and have already been established as a common practice in many such areas. In urbanised areas, where the communal water supply pressure is low or in high-rise buildings, a hydro-pneumatic water supply system will be most useful. Lastly, water-saving devices can be applied in most contexts.
In the case of rainwater harvesting systems and grey water reuse systems, institutional support is needed for effective large-scale implementation. The forms of institutional support may include and are not limited to:
- Guidelines for design and installations of rainwater harvesting systems
- Guidelines for preliminary water treatment and/or water purification for drinking (applicable for regions with scarce water resources and limited communal water supply)
- Guidelines and regulations related to environmental health i.e., prevention of mosquito breeding in rainwater/grey water storage tanks/containers.
To support the implementation of hydro-pneumatic water supply systems, capacity building through training workshops will help establish a pool of local skilled technicians to design, install and maintain the systems. Incentive programs and demonstrations are helpful to promote large-scale deployment of these technologies.
In the case of water-saving devices, awareness raising programmes by local governments or NGOs will be the most useful first step. These activities help the general public understand the benefits and create buy-in. Furthermore, it is useful to introduce and implement labelling system for water saving devices. An example is the Water Efficiency Labelling Scheme by the Singapore Public Utilities Board. Labelling schemes such as this are useful to sustain public interest and promote the implementation of water-saving products and the related technologies, which help them become mainstream in the market.
Water efficiency technologies and practices have, in general, been implemented in most regions of the world. Using simple forms of water metering for individual buildings is a mandatory practice in many urbanised areas, because municipal governments recognise that the practice can significantly influence user behaviours in conserving water. Two-thirds of Organisation for Economic Co-operation and Development (OECD) member countries have already installed water meters at more than 90% of single-family houses (Brandes et al., 2010). The complex application of sub-meters to major water-consuming systems in largescale buildings requires additional investment and coordination efforts. Therefore, sub-meters are not as popularly implemented. However, their benefits have been recognised, and the implementation rate has been increasing, especially in water-scarce urban areas, such as Singapore.
Due to their tangible benefits and simplicity of installation and operation, rainwater harvesting systems are widely applied in rural setting and small towns, where a municipal water supply is limited or not available.
Grey water reuse is also a popular practice in its simplest form, in which grey water is manually stored for subsequent manual usage. Grey water reuse systems require additional space, an additional piping network and treatment equipment. Therefore, the technologies do not enjoy the same widespread implementation as rainwater harvesting systems do. The OECD, however, projects that more city governments will support and promote the implementation of grey water reuse in their cities, as they face “the increasing mismatch between the available water resources and rising demand, in both OECD and developing countries” (OECD, 2009).
Hydro-pneumatic water supply systems area proven technology to save electricity and lower pressure surges in water supply systems, without a large capital outlay. Therefore, the technology enjoys good market penetration, especially in high-rise buildings in urban areas, and buildings in areas with lowpressurised communal water supply, such as Calcutta, India and other cities in developing countries.
Low-cost water saving devices, such as water tap flow regulators and efficient shower heads, are widely implemented and have large market potential in both developed and developing countries. In the District of Saanich, British Columbia, Canada, the government initiated the Tap by Tap Energy and Water Saving Fixture Exchange programme to allow resident to exchange their shower, bath and kitchen faucet fixtures with a set of water saving ones. High-efficiency shower head, kitchen faucet aerator and bathroom faucet aerators are among the new set of water saving devices on offer. The objective is to help residents reduce their daily water consumption by 50% (District of Saanich, 2010). Dual flush low capacity flushing cisterns and water efficient urinals also have good potential to develop a major market segment for new buildings. Water efficient irrigation systems, however, have their market share limited to higher-end buildings.
Water efficiency technologies contribute to environmental and resource protection through direct reduction of water and potable water consumption in buildings.
Energy consumption is also reduced by reducing the use of clean water and potable water in buildings. The saving is achieved not only through reduced on-site water pumping, but through reduced energy requirements to treat the water from the water treatment plant, transfer the water to end users, and treat discharged wastewater from buildings. Furthermore, hydro-pneumatic water supply systems are reported to save not only water but also up to 40% of the energy used by conventional water pumping systems (UNEP SBCI, 2010).
Rainwater harvesting systems also reduce the capacity stress to the storm water system. A largescale deployment of the technology will help reduce surface storm water runoff and cut down peak discharge to the urban drainage systems. The resulted water and energy savings can be translated to tangible economic saving to both the local government (by reducing infrastructure-related expenses)and to homeowners who save on water bills. Rainwater harvesting systems, grey water reuse systems and the use of dual flush toilets directly engage end users to conserve water, resulting in building awareness and helping to instil positive environmental-friendly habits and practices in society at large.
The financial requirements vary depending on the specific technologies, as well as the availability and suitability of a technology in a region. For example, in less dense village or town settings, the feasibility for implementing rainwater harvesting systems is high. The investment required for such systems is low, due to the availability of roof space and the already-in-place gutter and down pipe systems. The costs to the end-users are minimal, including water storage tanks, the optional detachable down pipes, as well as necessary maintenance. Rainwater harvesting systems in high-rise and high density urban environments, nevertheless, may cost more and are less cost effective. More sophisticated systems are required to cater for a small ratio of roof area over the number of users.
Some indicative costing examples are presented below. A rainwater harvesting system with an underground tank in Singapore costs about S$1,250/m3, not including costs relating to excavation, backfilling, pipes connection, pump, filter, etc. (DLS, 2008). Alow-flow shower head costs about US$5 in the Caribbean region. Tap water flow regulators prices range from US$1.4–$4 for a domestic faucet aerator in the US, and about R95 in South Africa. A conventional water meter’s price ranges from S$1,000 to S$3,000 each, and a digital meter’s price ranges from S$3,000 to S$5,000 per unit in Singapore.
BCA (2007). Green Building Design Guide – Air-conditioned Buildings. Singapore: Building and Construction Authority.
Brandes M. O., Renzetti S., and Stinchcombe K. (2010). Worth Every Penny:A Primer on Conservation-Oriented Water Pricing. POLIS Project on Ecological Governance, University of Victoria. [Online]: www.allianceforwaterefficiency.org/.../POLIS-Primer-on-Conservation-Rate- Structures-May-2010.pdf
District of Saanich (accessed on 20 Mar. 2011). Tap By Tap Energy and Water Saving Fixture Exchange. [Online]: http://www.saanich.ca/living/climate/tapbytap.html
DLS. (2009). Green Building Products and Technologies Handbook. Singapore: Davis Langdon & Seah Singapore Pte Ltd.
Government of Western Australia (2010). Approved Grey Water Reuse Systems. [Online]: www.public.health.wa.gov.au/cproot/1342/2/Approved%20Greywater%20Reuse%2...
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OECD (2009). Alternative Ways of Providing Water: Emerging Option and Their Policy Implications. Organisation for Economic Cooperation and Development: Working Party on Global and Structural Policies.
UNEP SBCI (2010). The ‘State of Play’ of sustainable buildings in India. Paris: United Nations Environment Programme, Sustainable Buildings and Climate Initiative, Paris. [Online]: http://www.unep.org/sbci/pdfs/State_of_play_India.pdf