Unfortunately, it depends on the rest of your diet, and your activity. Specifically, your carb intake and your cardio. If you want to encourage some water loss, drop the carbs a bit. So, eat less breads, grains, pastas, potatoes, whatever.
Yeah, that's why those things aren't acutally too 'smart'. If it's the kind that you stand on barefoot or whatever, it can be significantly swayed based on your hydration levels, or even the food you ate at your most recent meal. If you go to a gym, ask a trainer about getting a bodyfat skin caliper test. It's a more accurate method.
Better yet, forget about the number of your bodyfat, and base your results strictly on a specific outfit. Pick a t-shirt and a pair of jeans, and try it on twice a month. If you see and/or feel results when you're wearing the outfit, you're headed in teh right direction.