. Engineers had considered installing the world's first triple-deck elevators, but the final design called for double-deck elevators. The double-deck elevators are equipped with entertainment features such as LCD displays to serve visitors during their travel to the observation deck. The building has 2,909 stairs from the ground floor to the 160th floor. Plumbing systems The Burj Khalifa's water system supplies an average of of water per day through of pipes. An additional of piping serves the fire emergency system, and supplies chilled water for the air conditioning system. Air conditioning The air conditioning system draws air from the upper floors where the air is cooler and cleaner than on the ground. At peak cooling times, the tower's cooling is , equivalent to that provided by of melting ice in one day. Water is collected via a condensate collection system and is used to irrigate the nearby park. Window cleaning To wash the 24,348 windows, totaling of glass, the building has three horizontal tracks, each holding a bucket machine. Above level 109, and up to tier 27, traditional cradles from davits are used. The top of the building is cleaned by a crew that uses ropes to descend from the top to gain access. Under normal conditions, when all building maintenance units are operational, it takes 36 workers three to four months to clean the entire exterior. Unmanned machines clean the top 27 additional tiers and the glass spire. The cleaning system was developed in Melbourne, Australia, by CoxGomyl, a manufacturer of building maintenance units, at a cost of A$8 million. Features The Dubai Fountain Outside the Burj Khalifa, WET Enterprises designed a fountain system at a cost of Dh 800 million (US$217 million). Illuminated by 6,600 lights and 50 coloured projectors, it is long and shoots water into the air while accompanied by a range of classical to contemporary Arabic and other music. It is the world's largest choreographed fountain. On 26 October 2008, Emaar announced that based on results of a naming contest the fountain would be called the Dubai Fountain. Observation deck An outdoor observation deck, named At the Top, opened on 5 January 2010 on the 124th floor. At , it was the highest outdoor observation deck in the world when it opened. Although it was surpassed in December 2011 by Cloud Top 488 on the Canton Tower, Guangzhou at , Burj Khalifa opened the 148th