Abstract
To prevent the bacterial contamination of the drinking water, we developed a periodical draining machine system which were composed of the electromagnetic valve and the time switch. The machine system is able to replace standing water with fresh water on optional volumes and intervals. The total bacterial numbers of standing water were counted as an indicator of the bacterial contamination. The number of total bacteria were reduced to less than 5 per ml by working the machine system on 6-hour-interval with replacing twice as much as standing water, although more than 103 per ml of the bacteria were found when the system was not operated. It was demonstrated that the periodical draining of the machine prevented the drinking water in auto-watering piping from bacterial contamination.
