填空题

Water is tasteless, odorless, and nearly colorless (it has a slight hint of blue). It is a 【B1】 that is essential to all known forms of life in its pure form. Water is 【B2】 on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also 【B3】 clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is 【B4】 moving through the cycle involving evaporation, precipitation , and runoff to the sea. Water fit for human 【B5】 is called potable water. This natural resource is becoming 【B6】 in certain places as human population in those places increases, and its availability is a major social and economic 【B7】 . Drinking water is water that is intended to be drunk by humans. Water of 【B8】 quality to serve as drinking water is called potable water whether it is used as such or not. Although most fresh water sources are drinkable 【B9】 humans, they can be a disease vector or cause long-term health problems if they do not 【B10】 certain water quality guidelines. Most nations have water quality regulations for water sold as drinking water, although these are often not strictly 【B11】 outside of the developed world. Virtually all municipal water systems deliver a single quality of water, whether it is to be used for drinking, washing or landscape irrigation. In the United States, public drinking water is 【B12】 by the Safe Drinking Water Act (SDWA). Among other 【B13】 , it protects the right of employees to report potential 【B14】 . Within 30 days of any retaliation, a whistleblower can file a complaint with the Occupational Safety and Health Administration (OSHA). So far 【B15】 bacterial is concerned, the usual test is for a count of (more often than not harmless) bacteria, it 【B16】 that these serve as an indication of water pollution. Water purification is the removal of contaminants from 【B17】 water to produce drinking water that is pure enough for humans. Many contaminants can be dangerous—but 【B18】 the quality standards, others are removed to improve the water’’s smell, 【B19】 , and appearance. It is not possible to tell whether water is safe to drink just by looking at it. Simple procedures such as boiling are not sufficient for treating water from an unknown source. Even natural spring water— 【B20】 safe for all practical purposes in the 1800’’s—must now be tested before determining what kind of treatment is needed.