What could be the cause of chronic dehydration with slightly low potassium and sodium? i drink 90oz of water a day and put salt on almost all my food.

Not dehyration: You're not dehydrated, you're diluted. Your excessive fluid intake is causing your electrolyte imbalance. Eating salt will not raise your serum sodium for physiologic mechanisms that can't be explained here. This is called "dilutional hyponatremia" - you can google it.

Fluid balance: The explanation may be complex. Albuterol in high doses can cause low blood potassium. Otherwise, if you are drinking over 90 oz fluid per day and adding salt, and are still appearing dehydrated to your practitioner, then you must be losing fluid and some Na and K from your body somewhere. Possibilities are GI, skin, or kidneys. Some kidney dz cause just that: fluid loss, Na loss, and K loss.