Your concerns about your grandmother’s health are very significant.  Dehydration is serious and can lead to other complications.  Alzheimer's disease affects the ability to coordinate the tongue, lips and jaw.  It is very common for individuals with Alzheimer's disease to develop swallowing disorders, or dysphagia.  It is important to assess your grandmother’s overall situation to determine if any new medications or changes in her level of consciousness could be affecting her ability to swallow.  In addition, her body and head position are essential when engaging her to take a drink.  Forcing her to drink could be distressing to her, which may prevent her from being able to relax and successfully complete the task.          One option is for your grandmother to have a speech pathologist conduct an assessment.  A Videofluoroscopic Swallow Study may help determine the source of the problem.  Also a speech pathologist can help make recommendations for a new swallowing program to improve the fluid intake for your grandmother.  There is a stage of Alzheimer's when swallowing becomes too difficult entirely.  Many individuals with Alzheimer's will become candidates for some form of tube feeding, either nasogastric tube through the nostril or a PEG tube into the stomach.  There are certain risks with such interventions, and so the people making health care decisions need to be very careful in choosing the best course of care.    It is highly recommended that you seek consultation with her physician.  There could be medical reasons apart from the Alzheimer’s disease that could be causing difficulty for your grandmother.  The longer the issue is not addressed by a medical professional, the more precarious the situation could become for your grandmother and the family.