Ellis and her family of 4 will be traveling for 8 hours going and 8 hours coming home = <<8+8=16>>16 hours total.
Each person needs 1/2 a bottle of water each hour, so 1/2 a bottle x 16 hours = <<1/2*16=8>>8 bottles.
There are 4 people traveling so 8 total water bottles for each person x 4 people = <<8*4=32>>32 total water bottles.
#### 32