An Architect's Guide for Sustainable Design of Office Buildings
6. Building Water Use
Canada has 20% of the world's freshwater. On average, Canadians use 390 litres a day each - the second highest water use per capita of all developed countries.
Reductions in water use are environmentally desirable in that they decrease the load on both water supply and waste treatment facilities, leading to lower requirements for energy and treatment and to improve the quality of sewage effluents. The opportunities for direct financial savings are extremely variable. Considering PWGSC's situation, total expenditure on water in the National Capital Area was over $12 million in 1995-96. When combined with other federal facilities across the country, this figure would approach $100 million annually. The implementation of water efficiency measures could reduce water consumption by up to 50%.
Water demand in Canada will continue to increase as the population rises over the next decade and will place severe stress on existing infrastructures for the collection, treatment and distribution of water to urban centres. Moreover, although the cost of water is currently relatively inexpensive, the cost of maintaining the existing infrastructure and providing additional supply to meet increasing demand will manifest itself in increased price of water supply to all users.
In meeting the dictates of sustainability:
- The amount of potable water used to support building-related activities should be reduced through the deployment of water efficient appliances;
- Separating and retaining of grey-water should be considered for appropriate applications.
The key strategies for building water conservation are:
- Using less potable water to accomplish sanitary tasks through the use of more efficient appliances;
- Communicating water use to occupants;
- Using water of lower quality such as reclaimed waste water effluent, grey water, or run-off from ground surfaces for toilet flushing or irrigation.
6.1 Specifying Water Efficient Appliances
Reducing the amount of potable water through the use of more efficient appliances.
The following devices have been identified to be water saving:
Low Flush Toilets
Flush valve toilets and automatic flush urinals are the single largest users of water in many buildings. In offices, toilets may account for 50% of total use. This can be easily reduced by 60% by specifying water conserving flush toilets which are now widely manufactured or adjusting flush valves for minimum acceptable volume.
Toilets and other low flow appliances will reduce water demand without requiring that the user change the pattern of use.
Current CSA standards have fixed the water consumption of toilets at 13.5 L/flush, but market demands have seen an emergence and use of 6 litre water carriage models.
Full flow lavatory faucets typically deliver 0.25 to 0.3 L/s. Low-flow faucets utilize aeration to function as well or better with far less water. Lower flows achieve a range from 0.03 to 0.16 L/s.
Other features to lower the usage volume are the foot operated faucet and the electronic sensor faucet, both of which disconnect the water flow more reliably than if left to the user.
Hot Water Conservation
Hot water supply is another important cause of water and energy waste in buildings. Where lavatory fixtures are located remote from the hot water source more water is often wasted to bring hot water over the distance than is actually used for washing.
Building water use can be reduced by:
- Reducing the amount of potable water used to support building-related activities through the deployment of water efficient appliances;
- Specifying water conserving flush toilets with a maximum 6 Litres/flush, which meet appropriate CSA Standards;
- Specifying spring loaded lavatory fixtures having a maximum flow rate of 0.14 Litres/second;
- Specifying urinals having a maximum flow rate of 0.06 Litres/second and fitted with manual spring loaded, flush valves or automatic, motion sensor valves;
- Considering the use of electronic proximity devices for controlling lavatory fixtures;
- Shower fixtures should be rated for a maximum flow rate of 0.16 Litres/second;
- Considering the collection, retention and use of rainwater for appropriate applications rather than diverting it to the nearest storm drain.
6.2 Water Conservation Management
It will become increasingly important to communicate the reasons and benefits underlying water conservation strategies to building users.
Building design can assist in informing users of their actual water savings as well as their responsibility by:
- Providing appropriate signage in rest-room to indicate the high priority placed on water conservation;
- Providing water metering in buildings to determine how much water is being consumed.
6.3 Considering Water Reuse
Grey-water, in combination with rainwater, can be stored, filtered and integrated into the water supply to toilets, with or without the possibility of waste heat recovery. (See Section 3: Site and Landscape)
Building type, size and the number of its occupants plays a large role in determining the quantity of potable water used, waste-water generated and the feasibility of waste water reuse. The amount of grey-water generated in a building is typically directly proportional to the economic feasibility of its reuse when it is treated on site.
- Water Management Strategy for Property and Facilities Management, DRAFT, PWGSC, RPS, March 1996, p. 4. (back to 1)