WC cistern water displacement devices are available in all countries, albeit only a stone or brick in some cases. More imaginative in the UK, with a typical flush of 6-9 l, is the use of the plastic bags, 'Hippo' and yellow sponges, 'Soggy Doggy', that have been distributed free by water companies to encourage their customers to conserve water. These devices either displace or retain water within the WC cistern to reduce the volume of water that is flushed. Water displacement devices such as dams and bags are very popular in the USA where cisterns are generally much larger and less cluttered than UK cisterns. This is because American cisterns have traditionally flushed over 15 l of water using compact cistern outlet valves: 'flappers'. Unfortunately it has been found that some displacement devices may actually increase the flushing volume if they are fitted such that they obstruct the flush volume limiting aperture in a siphon. If the entire volume of water in the cistern is necessary to clear the WC pan, a reduced flush volume may not be effective, resulting in the repeated flushing of the cistern and hence an increase in the amount of water used, rather than a decrease.
WCs can be flushed with water using compressed air assistance. Some such cisterns use the pressure of the mains water supply to compress a volume of air above the stored water. When the water is released into the bowl it has a much greater velocity than from a conventional gravity-operated cistern. These products are used in parts of France and the USA. To be used efficiently these cisterns need to be matched to WC pans that can use the higher velocity water effectively. Another type of water and compressed air toilet uses water to rinse the bowl and compressed air to evacuate the contents. This type is used in many types of building in the USA.
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Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.