Can not drinking water for 8 hours a day during work cause mouth blister?

I can not link these as cause & effect. Certainly some who does not drink water for 8 hours can develop one, just like someone who drinks 8 oz/hr. They are often caused by viruses you plant in your mouth from your fingers.

A viral infection or contact allergy to food or other allergen may cause blisters. Although important to hydrate during the day, it’s unlikely 8 hours of non-hydration will cause blisters day or night. However, it’s possible that Mouth Breathing day & especially night can cause severe dry, chapped lips. Seek a consult with your dentist. An Oral Myofunctional Therapist can help with mouth exercises

We all have pathogens that live in our mouths and oral tissues. Dehydration can further stress tissues, along with other stressors. All of the tissues in your body would benefit from staying adequately hydrated.