Bodyweight Fluctuations: how much %/day is to be expected??

So, I’ve been weighing myself several times a day (as the fancy strikes me) and noticed that my bodyweight typically fluctuates about 5 pounds over the course of the day (about 3%). I notice that I’m most often at the 185lb. mark. I’m going to assume that this is average for me and this amount of weight fluctuation is not abnormal.

Recently, I’ve been noticing that I’m fluctuating more than 10 lbs. between days! Some days I’ll be at 195 and others at 178ish. Granted, during this period, my activities have been significantly different than before (less crap foods, indeed, less food in general and more exercise than I’m accustomed to). I suppose that fluctuation is only 5-6%, but is that normal/healthy? But 20 lbs. between two days? I certainly don’t feel any different than I normally do.

The only explanation I can think of is that I’m catching the extremes of the tolerance of the scale: i.e. 2% on this side plus 2% on the other side combined with the normal 3% change.

Several pounds of day-to-day fluctuation are to be expected, and it’s not what you eat but what you drink. The amount of water that goes through you in a day dwarfs the amount of food. You can’t possibly eat enough in a day to make a significant overall difference in your weight, but if you do snack on something salty, and follow it up with extra water (which furthermore you’ll tend to retain because of the extra salt), you’ll weigh quite a bit more the next day.

Plus, don’t take your scale’s measurement as gospel. There’s a substantial margin for error in those things. Ten pounds seems like a lot; maybe it’s your scale that’s going bad. But if you do exercise (and sweat) quite a bit, you’ll weigh less than if you eat potato chips and drink a lot of water.