Plain water can be hard for your body to do anything with especially if it’s cold and your body has to warm it up first. But no salts or sugars can mean it’s hard for your body to absorb it. You really should attempt some fiber or protein as well and give your stomach acid something to work on.
Dehydration can also cause nausea, but I haven’t had success with only drinking water for breakfast.
Plain water can be hard for your body to do anything with especially if it’s cold and your body has to warm it up first. But no salts or sugars can mean it’s hard for your body to absorb it. You really should attempt some fiber or protein as well and give your stomach acid something to work on.