求翻译：采用真空排污系统的情况下，每次用水1～2L；现行冲洗系统，包括较为节水的延时自闭冲洗阀和水箱冲洗，每次用水平均为8 L左右，真空排污系统较传统重力卫生系统节水效果明显，用水比率为1：4。是什么意思？

Case of vacuum sewerage systems, water for every 1~2L; existing irrigation systems, including more time-lapse self-closing flush valve for water saving and water tank washing, each time the average is around 8 l of water, vacuum sewerage systems compared to traditional health system of water-saving effect of gravity, water use ratio of 1:4.