Drinking all day and still not feeling hydrated is more than likely another medical issue; I believe the symptoms of diabetes is excessive thirst, craving water and never feeling hydrated.
Symptoms of a potassium deficiency Is normally fatigue rather than a feeling of thirst; potassium supplements won’t do any harm, as long as taken within reason; normally excess potassium is excreted via the kidneys.
It’s probably easier to maintain a good potassium level via your diet, such as Milk, Cheese, Eggs, Bananas, Baked Potatoes, Fish, Tomatoes and most leafy green vegetables.