填空题. Humanity uses a little less than half the water available worldwide. Yet occurrences of shortages and droughts are causing famine in some areas, but industrial and agricultural by-products are polluting water supplies. 1 Since the world's population is expecting to double in the next 50 years, 2 many experts think we are on the edge of a widespread water crisis. But that doesn't have to be the outcome. Water shortages do not have to trouble the world—if we started valuing water more than we 3 have in the past. Just like we began to appreciate petroleum more after 4 the 1970s oil crisis, today we must start looking at water from a fresh economical perspective. We can no longer afford to consider water a 5 virtual free resource of which we can use as much as we like. 6 Instead, for all uses except the domestic demand of the poor, governments should price water to reflect their actual value. This means 7 charging a fee for the water itself as well as for the demand costs. 8 Governments should also protect this resource by providing water with more economically and environmentally sound ways. 9 Often the cheapest way to provide irrigation water in the dry tropics is through small-scaled projects, such as gathering rainfall in depressions 10 and pumping it to nearby cropland.