I think the first two weeks are definitely mostly water weight. I've been reading a lot on how cutting out sugar/carbs or caffeine signals the body to let some water go. And if you are eating at a deficit, you will be burning fat too. It sounds like you are getting enough water - 3 L a day seems like plenty to me
If your deficit is over 300-500 cals a day, you might be losing a little muscle mass too. I totally recommend adding some weight training to your routine to help with that.
Also, I have a scale that measure my body fat % . You can find a decent one for around $30-40 and it will give you your weight, % body fat and % water. They aren't super accurate, but the trends are! I love seeing that body fat % go down more than the weight.