Body water drift in smart scales

Hi - this is a bit off topic for Intervals, but I thought one of the very smart people here might have some insight. (I will also send a question to Withings).
I have a Withings smart scale. I recognize that the calculations are all influenced by how hydrated I am, so I don’t put much stock in day to day variations in lean mass, body fat %, etc. However, my assumption was that trends over longer periods - months, a year - would be more accurate as day to variations in body water would be in the noise. I was looking at the past year, and was pleased to see a decrease in body fat %. However, I then looked at Water over the same year and saw the same trend.
It’s possible that I’ve been genuinely improving my hydration over the past 12 months - but I suspect this isn’t real, which makes me think it’s some kind of drift in the scale. Anyone have any knowledge about this?

Thanks,
Michael

body mass was constant?

No definitely not over an entire year.

Just a guess…percent-wise you have more bones now, bones are less waterish then fat or muscles, so your overall water % can drop. But that is just a guess.