The living roof, seawater heating and cooling, on-site water treatment and fish habitat built into the foundation of the West Building make it one of the greenest convention centres in the world. The Centre recycles an average of 180,000 kilograms of materials annually, nearly half of the total volume of waste generated. It avoids canned goods, disposable utensils and dishes, and donates leftover food to local charities. The "living roof" is the largest in Canada and the largest non-industrial living roof in North America. The roof landscape is designed as a self-sustaining grassy habitat characteristic of coastal British Columbia, including 400,000 native plants and 4 colonies of 60,000 bees each which provide honey for the public plaza restaurant. No public access is allowed to the roof, which made it possible to create a fully functional ecosystem with natural drainage and seed migration patterns using the roof's architectural topography. The landscape functionally connects to nearby Stanley Park via a corridor of waterfront parks. Irrigation to the roof is provided by the building's wastewater treatment plant. In the event that the roof irrigation demands exceed the capacity of the wastewater treatment plant, make-up water can be provided by a reverse osmosis desalinization plant drawing and treating seawater pumped from the harbour as well as municipal water through an air gap connection to the storage tanks, as needed. All wastewater from washrooms, retail, and restaurant activities in the building is reclaimed and recycled for use in toilet and urinal flushing, and green roof irrigation. The treatment facility uses a membrane bioreactor process, manufactured and supplied by GE/Zenon, consisting of two 2-zone (anoxic/oxic) bioreactor tanks (with internal recycle) and an ultra-filtration (hollow-fibre) membrane tank, followed by a chlorine contact tank that serves to remove colour and disinfect the reclaimed water. The treatment system is designed for an average daily flow of per day, and maximum flows of up to per day. With the City of Vancouver 2012 commercial metered water and sewer rates at $2.803 and $1.754, respectively, the convention centre can save over $21,000 per month in utility fees through water reuse. One of the biggest operating challenges when the facility first started up was the ability to maintain the treatment plant bacteria in a healthy condition during lengthy periods (e.g. late December through mid-January) with limited wastewater to feed the treatment plant due to limited convention activity and concurrent wastewater generation within the building; however, once the restaurants in the building were established this challenge was resolved.