Why the scale alone can't tell you
Body weight is a composite of fat, muscle, water, and gut contents. A single reading has no way of separating which component moved -- yet water weight can swing by several pounds in a day from sodium, carbohydrate intake, hormonal cycles, or hydration status alone.
Signals that point to water, not fat
A sudden multi-pound shift after a single high-sodium meal, a swing tied to the menstrual cycle, or a rebound after a low-carb stretch (carbs bind water at roughly 3g of water per 1g of glycogen) all point toward water rather than fat.
Signals that point to real fat loss
A gradual, multi-week downward trend in your weekly average weight, paired with improving measurements or how clothes fit, is a stronger signal of genuine fat loss than any single day's number.
The practical fix
Weigh daily at a consistent time (morning, post-bathroom, before eating), then track the 7-day rolling average instead of any individual reading. This single habit removes most of the water-weight noise from your progress picture.