Your jars should not be going through a significant amount of water in a short time. Of course, all installations are different, but you should not have to be adding water every day. In my experience, the water contained in a single jar Electrolyzer should last for 900 miles. I would fill it up (just add water) every 450-500 miles. If you think you're going through water too fast, you probably are.
One major reason for losing water fast is due to fast evaporation and boiling - make sure your Electrolyzer does not overheat.
The multi-cell structure, apart from being very energy efficient, is also a great solution to contain more water and go thru water very slowly in comparison. The water stays relatively much cooler, so much less loss due to heat and evaporation. Additionally, the sheer amount of water in 2, 4 or 6 jars gives a much greater range before you need to refill.
For more details, refer to the maintenance and installation chapters of the books and DVD's.