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I think such buildings will become more common in the future. First,
by making use of rainwater, a building owner can reduce the cost
of water used from the water supply. For example, rainwater can
be used for washing cars and for growing plants in gardens.
Second, collecting rainwater can be useful in times of disaster.
Due to damage to water pipes, supplies of water are sometimes
limited. In such cases, rainwater will help until normal conditions
return. Therefore, I think buildings that collect rainwater will
become more common in the future.
(*上記はあくまでも解答例です。)
