"a cubic structure" - Translation from English to Arabic

In Windhoek, a rising block tariff structure has been adopted: the first tier of six cubic metres of water costs N$7.13/m3; the second tier of six to 45 cubic metres during normal periods, and six to 36 cubic metres during times of water scarcity costs the full cost-recovery price of N$12/m3; beyond 45 or 36 cubic metres, depending on the water-scarcity level, users are billed N$22/m3.
In Windhoek, a rising block tariff structure has been adopted: the first tier of six cubic metres of water costs N$7.13/m3; the second tier of six to 45 cubic metres during normal periods, and six to 36 cubic metres during times of water scarcity costs the full cost-recovery price of N$12/m3; beyond 45 or 36 cubic metres, depending on the water-scarcity level, users are billed N$22/m3.