Why would i get a dry mouth after drinking lots of water?

Not sure: Dry mouth could be attributed to a number of different things. Systemic problem or medication comes to mine. I would seek care from a doctor to see if there is any issues that you need to be concerned with. Good luck.

Medication/ disease: You may be on a medication with dry mouth as a side effect. These would include diuretics, blood pressure medicine, antihistamines or more. Also you may have an underlying condition such as diabetes, thyroid disease, heart disease, or more. Please see a local physician for a full check-up...Take care...

Easy does it!: Saliva is important for digestion & to protect the hard & soft tissues of the mouth. When you are constantly chugging or even sipping water, the saliva gets diluted & loses its properties. If you're thirsty drink the water down in sufficient quantity to restore hydration but then stop long enough to allow saliva to regain its normal concentration in the mouth. If still dry use saliva substitute.