Dry mouth

I recently upped my dosage to 300 mg and my mouth is now the Sahara desert. I am drinking litres of water a day (like, 10x filling up a 4L bottle) and am finding no relief. I just gotta pee more. My dentist recommended a moisturizing mouthwash, which definitely helps temporarily. I just wish it lasted longer than 30 mins after using it. Any tips?