Is this Normal when switching to Low Carb from Another plan

[HadEnough]

I was previously on WW and was not having the success I wanted so I switched back to calorie counting and moderate carbs (under 100g). I have lost 4 pounds in 2 days. Is this water weight AGAIN, like when you start any plan?

[Rosinante]

Depending on how many carbs you were eating beforehand, it can be, as some carby food, however well within your calorie budget you are, can hold onto water for some people; for me.
Unless you ate 7,000 calories fewer than you need on those days, it cannot be 2lbs of fat; but 2lbs of excess water is 2lbs of weight your joints don't need the strain of bearing, so it's all good.

[AliceInFatland]

Yes. When you start a low-carb diet in particular, you WILL lose water weight. Each gram of glycogen is connect to four grams of water. When you stop eating carbs, your body starts using up its glycogen supply, and there goes all that water.