Pollution of water supplies is usually due to poor health conditions close to water sources, sewage 【T1】 1into the sources themselves, leakage of sewage into 【T2】 2 systems or pollution with industrial or 【T3】 3waste. Even if a piped water supply is safe at its source, it is not always safe by the time it reaches the tap. Intermittent tap water supplies should be 【T4】 4as particularly suspect.
Travelers on short trips to areas with water supplies of uncertain 【T5】 5should avoid drinking tap water, or 【T6】 6water from any other source. It is best to drink hot drinks, bottled or canned drinks of well-known brand names—international 【T7】 7 of water treatment are usually followed at bottling plants. Carbonated (含二氧化碳的) drinks are acidic (酸性的), and slightly safer. 【T8】 8, and that their rims (边缘) are clean and dry.
Boiling is always a good way of treating water. 【T9】 9. Portable boiling elements that can boil small quantities of water are useful when the right voltage (电压) of electricity is available. 【T10】 10. 【T1】