I have the tanita scale that measures weight/body fat, and I love it. I've owned it for about 2 years, never had a problem with it, and only changed the battery once. I have two kids that are constantly jumping on it, spilling water on it from the tub, etc, so there's alot to be said for its durability! It measures body fat by sending an electrical impulse through your body, weighing you, and then computing those results with the info you put in, such as height and sex. I think they are very accurate-even though I don't like the results I get
. I don't get any crazy variations, and they work the same way as the one the trainer at my gym used on me-the one you hold out in front of you. The only more accurate way that you can measure body fat is taking a million caliper measurements. I payed 39.95 for mine at an eckerds, I'm sure they can be found a little cheaper elsewhere. The only drawback is that while it has a setting to measure kids, it's impossible to do, because their little feet can't fit correctly on the metal spots.
While I do believe a scale could distinguish fat/water/muscle by measuring density, I wouldn't bother with the water weight-our bodies contain so much water, and the amount we retain varies so widely not only day to day, but literally hour by hour, so honestly what good would it do to know? Even if I did know I was retaining x amount of water weight, that won't make my jeans fit any looser