In my car the quart jar is enough for 900-1000 miles. My neighbor drives at least 6-8 weeks around town before she needs to add water.

Another thing you will learn about in the books or DVD's is the "multi-cell" arrangement. I have driven with it (six jars) for a whole FOUR MONTHS and only 20 or 25 percent of the water got used up. I then washed it all out and put fresh water and everything, but I could have probably driven up to 6-8 months WITHOUT EVER TOUCHING the system. Now it starts to look more like standard automotive maintenance (3-5 months) or even better, doesn't it?