[al:新概念英语（四）] [ar:MP3 同步字幕版（英音）] [ti:Water and the Traveller] [by:更多学习内容，请到chazidian.com搜索“新概念”] [00:01.51]Lesson 38 [00:03.45]Water and the traveller [00:11.95]What does this text describe? [00:16.88]Contamination of water supplies is usually due to poor sanitation close to water sources, [00:23.71]sewage disposal into the sources themselves, leakage of sewage into distribution systems or contamination with industrial or farm waste. [00:34.92]Even if a piped water supply is safe at its source, it is not always safe by the time it reaches the tap. [00:43.24]Intermittent tap-water supplies should be regarded as particularly suspect. [00:49.68]Travellers on short trips to areas with water supplies of uncertain quality [00:55.51]should avoid drinking tap-water, or untreated water from any other source. [01:01.52]It is best to keep to hot drinks, bottled or canned drinks of well-known brand names- [01:07.76]international standard of water treatment are usually followed at bottling plants. [01:13.72]Carbonated drinks are acidic, and slightly safer. [01:17.82]Make sure that all bottles are opened in your presence, and that their rims are clean and dry. [01:25.14]Boiling is always a good way of treating water. [01:28.87]Some hotels supply boiled water on request and this can be used for drinking, or for brushing teeth. [01:36.44]Portable boiling elements that can boil small quantities of water are useful when the right voltage of electricity is available. [01:45.31]Refuse politely any cold drink from an unknown source. [01:50.80]Ice is only as safe as the water from which it is made, [01:54.55]and should not be put in drinks unless it is known to be safe. [01:59.25]Drinks can be cooled by placing them on ice rather than adding ice to them. [02:05.33]Alcohol may be a medical disinfectant, [02:08.62]but should not be relied upon to sterilize water. [02:12.47]Ethanol is more effective at a concentration of 50-70 percent; [02:18.61]below 20 per cent, its bactericidal action is negligible. [02:24.30]Spirits labelled 95 proof contain only about 47 per cent alcohol. [02:31.21]Beware of methylated alcohol, [02:34.07]which is very poisonous and should never be added to drinking water. [02:39.39]If no other safe water supply can be obtained, [02:42.72]tap water that is too hot to touch can be left to cool and is generally safe to drink. [02:49.73]Those planning a trip to remote areas, or intending to live in countries where drinking water is not readily available, [02:57.06]should know about the various possible methods for making water safe.