My daughter loves, loves, loves to drink water. Since she was about 5 months old, she’s experimented with drinking out of my glasses. Usually she ends up covered in water, but it makes her happy so we let her do it anyway.
It’s pretty entertaining to watch her with cups. She sort of gets the concept and knows which side she should be able to drink out of, but she tries to drink regardless of whether or not there’s anything in the cups. See exhibit A from last night*: