题目内容

______________ solutions such as solar-powered desalination plants are very useful.

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In the rich North, toilets using water are the largest single__________ on domestic water supplies.

It is not a must for the developing countries that currently lack adequate capital to __________ this wasteful practice.

They need toilets which can safely turn human waste into a smellless, soil-like ________.

However, almost 60 percent of the water is lost during the ________.