I started IF (16:8) on Monday, I was 84.8kg & as of today I’m 80kg apparently when I checked the scale, is this most likely water weight?
You’ll lose some water weight when you start as well as (likely) having less volume of food inside you.
An important thing to consider if your goal is weight loss is that as you continue and begin to burn fat, you should expect your body to retain the water that fat is metabolised into for a while - you’ll probably get frustrated as you notice the scales pause for days or weeks, but this is when you should push through it and keep going, and all of a sudden your body stops retaining the water from the burned fat and the scales will “whoosh” down dramatically, sometimes multiple kilos at once.
I like to use a tape measure to measure my waist and abdomen once per week, often when the scales haven’t moved at all or even gone up, I’ll have dropped a cm or two from my gut circumference.
Water weight. Carbohydrates take a lot of water to digest and function. That’s where the hydrate part of the name comes from. Eat fewer carbs and you will have no need to keep retaining the water. Keep eating the carbs and keep gaining the water weight back. Drink water anyway because it is your friend but you won’t retain if you eat less carbs.