- System Description
- Campus Context
- Goals and Targets
- Lessons Learned
- Future Learning
Image 12.1 Rainwater to Potable Water System Diagram
12.1 System Overview
CIRS is designed to be entirely water self-sufficient. All of the potable water in the building is supplied by the rain that falls on the building roofs. 1 Through a simple system, rainwater is harvested from the roofs of the building and stored in a cistern below the building. The rainwater is filtered and disinfected onsite and distributed through the building for potable water applications.
The annual rainfall pattern in Vancouver is one of moderate to large amounts of precipitation from late September to early June and near drought-like conditions from late June to early September. Fortunately, the periods of the lowest amount of rainfall annually approximately coincide with times that the student, staff and faculty populations at UBC are at their lowest. To provide a sufficient supply of potable water from late June to early September, large quantities of rainwater are required to be captured and stored during the rest of the year.
Vancouver has an approximate annual rainfall amount of 1226 millimeters per square meter. With a roof collection area on the building of 1000 square meters, 1,226,000 litres of rainwater can be harvested throughout the year. The estimated average demand for potable water in the building is 2,000 litres per day. The demand includes a variety of uses, such as sinks, showers, the Loop Cafe (drinks, cooking, cleaning), janitorial services and building maintenance. In addition to this amount, due to the extensive use of wood in the building, 57,000 litres of water are required to be continually available for the fire suppression system. Harvested rainwater is stored in a 100-cubic-meter cistern underneath the building.
1 Water falling on the living roof and vegetated areas is not used for potable uses in the building. (Water falling on these areas can carry too much particulate matter that could potentially damage the rainwater filtration and treatment system.
12.2 System Description
Step 1 – Collection
Rainwater is collected on the upper roof on the north and south wings of the building and channelled into the storage cistern underneath the building.
Step 2 - Storage
Depending on the potable water supply and demand, the rainwater is stored for up to three months (the cistern is sized to store a three-month demand). The longer storage time is possible due to the continual circulation of oxygen through the water, which reduces the growth of potential contaminant and the development of odour and discoloration.
Step 3 – Filtration
From the cistern, the rainwater is filtered through a three step process. The first step is a slow sand filter to remove larger particles, next is a fine filter to remove smaller particles and parasites, and finally an activated carbon filter which removes metals and organic contaminants from atmospheric contaminants.
Step 4 – Disinfection
After filtration, the water is disinfected through a two-step process. First, the water is exposed to ultra-violet light to kill any remaining pathogens, and then a small amount of residual chlorine is added.
Step 5 - pH adjustment
Rainwater in the lower mainland of British Columbia has a pH of about 4, which is below the regulated level for drinking water of between 6 and 9 ph. Sodium bicarbonate is injected into the water to adjust the alkalinity and reach the required pH level.
Step 6 - Treated water tank
After the water has been treated, it is stored in two tanks (for up to 12 hours, depending on demand) and delivered by pump through the building using a pressurized bladder system.
Monitoring & Back-up
It only takes a couple of hours for rainwater to move through the treatment process. The system is continually monitored and the water tested. If a problem is detected, the rainwater treatment system immediately shuts down, and water from the municipal system is supplied to the treated water tank and pumped into the building.
For additional information on the integrated water systems of CIRS, refer to Section 13.0 Reclaimed Water System for water treatment and reuse and Section 14.0 Landscape & Site for stormwater runoff.
Image 12.2 CIRS Integreated Water Systems Diagram
12.4 Campus Context
UBC Campus Plan
Potable water is currently provided to the UBC Point Grey Campus by the regional water supply system from a reservoir north of the city. The Campus Plan seeks to reduce the environmental impact of the University’s potable water use by reducing water consumption, maximizing reuse, matching water quality to use and seeking alternative sources.
Stormwater management is a significant concern on the campus, due to the cliff location and hydrogeology of the area. The University is shifting towards a natural systems approach to water management that values rainwater as a resource and identifies a number of applications for it on campus, including use in facilities, water features and irrigation. Collecting the rainwater instead of allowing runoff mitigates flooding and erosion risks throughout the campus.
UBC Campus Plan, Section 6.2 Sustainability Practices, Natural Systems Approach to Stormwater Management and Integrated Water System Planning, pg 39-40
UBC’s Campus design, construction and performance goals have long prioritized energy savings, and this priority is now extending to other areas, including water neutrality and waste management. CIRS’ extensive application of water collection and reuse strategies and technologies demonstrates the successful implementation on campus, opening the door for application in other buildings, clusters of buildings, or as campus-wide infrastructure. The CIRS project also provides valuable experience on navigating regulatory process and perceived water quality issues.
UBC Technical Guidelines
The rainwater to potable water system is covered by a range of Divisions in the UBC Technical Guidelines, and does contain conflicts with the requirements for the Living Building Challenge and the ecological and human health aims of sustainability. Specifically, the Guidelines require the application of chlorine as a disinfectant to the water supply.
Section 02660 Requirement for chlorine disinfection of water supply.
12.3 Goals & Targets
Table 12.1 lists the project goals and targets specifically related to the rainwater system. For a complete list of all the goals and targets for CIRS, refer to Section 4.0 Goals & Targets.
|3 - NET IMPACT||Eliminate on-site run-off.|
|8 - RAINWATER COLLECTION & USE||100 per cent of potable water requirements will be met with on-site collected rainwater.||100 per cent rainwater input.|
|10 - STORMWATER MANAGEMENT||"100 per cent stormwater will be treated, used or infiltrated on-site."||Zero stormwater output from site.|
Table 12.1 Goals and Targets for the Rainwater System
The use of the rainwater to potable water system at CIRS benefitted the project in the following ways:
The rainwater system is designed to raise awareness of the relationship between water supply and consumption. Inhabitants know that the potable water supply is finite and they will adjust their consumption patterns.
Reduced Potable Water Demand
The rainwater supply system reduces the demand for potable water from the regional water supply and the burden on municipal water infrastructure. The use of a localized water harvesting and treatment system reduces the amount of energy required to move water from centralized water treatment plants.
The closed loop collection system eliminates run-off from the building, thus reducing the risk of flooding and erosion on campus. Rainwater that is not collected for potable use (run off from the living roof) is discharged into a natural water feature and eventually infiltrate into the aquifer.
The system provides an onsite water source for the enhanced fire suppression systems required by the building code. A cistern for the fire protection system would have to have been provided if the rainwater cistern was not being provided.
The use of the rainwater to potable water system at CIRS was challenging of the project in the following ways:
Due to the public health concerns around potable water supply, Vancouver Coastal Health was consulted in the creation of the rainwater system. The inclusion of additional government agencies expanded the number and complexity of the regulations governing the design and construction of the rainwater system.. An agreement for continuing testing and monitoring of the water quality was required by the local health authority.
Conflict between Environmental Objectives and Drinking Water Regulations
Although chemical disinfection of potable water is specifically prohibited by the Net Zero Water imperative of the Living Building Challenge, the local health authorities required a chlorine residual in potable water to assure them that the public health is protected. The design team originally requested an exemption for the use of chlorine in the CIRS potable water treatment system, since other disinfectant measures were used however the local health authority enforced the requirement.
Pollution from Adjacent Sites
The design of a rainwater collection system must consider the impact of pollutants, such as particulates, from the local built and natural environment as these can affect the treatment system equipment and the water quality. Water collected from the roof has the potential to carry pollutants that may have come from activities on adjacent sites.
12.7 Lessons Learned
The experience gained through the use of the rainwater to potable water system for CIRS provided valuable lessons to apply to future projects. Some key lessons are:
Solve Multiple Problems
Look for opportunities to use one design solution to address multiple problems and to create multi-functional building systems and system components. The stored rainwater is used for as a backup for the fire suppression system, required to support the wood structural system.
Create Partnerships with Regulators
Consult with regulators early and often during the design process and work collaboratively to address their concerns and requirements. Be prepared to present alternate system designs and/or negotiate with the local authorities to find solutions.
Demonstration and Education Potential
The use of rainwater as the primary source of potable water also communicates very strongly to inhabitants and stakeholders that the project water supply is not infinite and that building inhabitants must use potable water conservatively. Innovative systems should be treated as learning opportunities and demonstrations for a broad network of stakeholders.
Additional lessons learned over the operational life of the building will be added at periodic intervals.