The water is cycled back into/through the system after it has been used.水经使用后又流回系统中循环。Evaporation reduced the water in the pond.池塘里的水经蒸发减少。The water is filtered to remove any impurities.这种水经过滤以去除杂质。The water is treated to reduce the levels of pollution in it.水经过处理可减少污染程度。