Yes, it can although should only be temporary. You will retain what you've lost through exercise. Talking plain (tap) water here.

However, fizzy drinks and soda can cause weight gain. Artificial sweeteners are the main culprits. That diet drink is not helping with weight loss, but the opposite. It's also well-known that regular and diet drinks such as cola, sprite, etc do not satisfy a thirst, so you drink more and more. Why they're recommended by one well-known weight loss company is difficult to understand. Same thing happens when you eat sugary foods.

Your metabolism should also be considered. Going to the bathroom is good. Your body is dealing with the extra fluid and will regulate itself. Fizzy drinks may also make you go to the bathroom more but the concern should be what's left behind.