The UN wants funds for emergency cholera treatment and for clean water supply systems and sewage plants.

BBC: UN launches appeal to fight Haiti cholera epidemic

It can end up in artificial water supply systems, including air conditioning systems, water services and cooling towers.

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On July 15, 1996, President Bill Clinton issued Executive Order No. 13010, in which he identified eight infrastructure systems critical to the nation's survival: telecommunications, electric power systems, oil and gas storage, transportation, banking and finance, storage and transportation, water supply systems, and emergency services (including medical, police, fire and rescue, and continuity of government).

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Computer systems that control the water supply and wastewater systems "have been the targets of probing by al Qaeda terrorists, " says Rep. Putnam, who cites U.S. law enforcement and intelligence agencies.

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Civil engineers design and develop the construction of transportation infrastructure and water supply and sewage systems, after attaining at least a bachelor's degree in engineering and several years of experience.

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The outbreak has been fuelled by the collapse of the country's health services, sanitation systems and water supply.

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For example, the supply of electricity, water and sewage systems are unpredictable and need to be appropriately protected from attack.

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With fresh water, we are working hard to establish biodiversity priorities and to demonstrate how incredibly important biologically rich, intact natural systems like rain forests are in ensuring a continued supply of clean water to human societies.

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It is spread through infected faeces and, once it enters the water supply, it is difficult to stop - especially in a country like Haiti which has almost no effective sewage disposal systems.

BBC: UN launches appeal to fight Haiti cholera epidemic