Does Water Affect Your Weight?

Absolutely. The human body is approximately 60% water so small swings in fluid balance will have a noticeable impact on scale weight irrespective of fat/muscle gains and losses. Some common scenarios where fluid balance can disrupt your weight measurements are listed below:

Carbohydrates - For every 1g of carbs stored in your body you will store a further 3-4g of water. This is one reason why low carb diets appear so effective in the early stages. A reduction in carb stores leads to a reduction in water and rapid weight loss... but it is primarily water.

Salt - High levels of sodium above your normal baseline will lead to increased water retention. This explains why going on a salty high carb binge after a period of dieting might lead to a disheartening overnight weight gain but again its primarily water

Hormones - Natural shifts and cycles in hormone levels can cause the body to retain more or less water. Particularly applicable to women. Again the scale weight rises and falls but it’s only water.

It's important to remember fat weight, lean weight and water weight are completely indistinguishable once you set on scale. Don't be alarmed by day-to-day fluctuations which are more than likely due to a shift in water and fluid balance. Instead focus on long-term trends.