From susosuwater.com:
As the body begins transforming into a fat-burning furnace, your metabolism is changing as well. Here’s why water is essential for your body as you continue on your ketogenic journey:
Drinking water replaces the water you lose through ketosis.
As I mentioned before, your body is losing much of its water storage as a result of the low carb diet. Ridding the body of carbs means flushing water out as well, and you need to replace that water to maintain your health
Drinking water alleviates the stress on your kidneys.
Since ketones are acidic and can get flushed out as opposed to being used as fuel, drinking water helps to keep your kidneys functioning as they should. Instead of forcing your kidneys to work harder, you’re supporting their role as they filter any lingering toxins
Drinking water improves fat metabolism
As you take in more water, you’re improving the process of beta-oxidation, or the breaking down of fats. This is because this process demands water molecules. As you burn fat, you’re using water, and without carbs, you need to consume more water to assist your body in effectively breaking down those fats