By 2025, water shortage will be a big problem for about 1.8 billion people. In a world where water resource is increasingly short, nations cannot afford to waste it. 【小题1】 After we use water in our homes and businesses, it is washed away, and takes many valuable resources with it.

Waste water is rich in carbon and nutrients. 【小题2】 A number of nations and major cities have already built waste water treatment plants. They can effectively recover nutrients and bio-energy, and produce “new water” that can be reused. But more than 80% of all waste water still currently flows into natural ecosystems, polluting the environment and taking valuable nutrients and other recoverable materials with it.

【小题3】 This is still better than the situation in smaller cities. In Latin American countries, those living in small and medium-sized cities at most treat it in the form of septic tanks(化粪池) that lack regular and proper maintenance.

Imagine that outside one of these small cities lies a lovely piece of land: on the surface it is aesthetically (美学地) built and provides habitats for local wildlife. Beneath the surface is wetland that treats waste water and produces energy.

The energy produced saved families from having to use firewood collected in the wild. This is not a dream project. 【小题4】 A team of scientists have been looking into the potential of the constructed wetland environments. Having analyzed 800 examples of biomass in more than 200 countries, they found that, depending on climate and the type of plant used in the construction of this type of wetland, up to 45 hectares of land could be irrigated with waste water. 【小题5】