I flew a CRJ 200 operated by a regional carrier.

FA came down the aisle with a drink cart and asked the woman in 1A what she wanted to drink. She said sparkling water. The FA pulled out a drawer and poured the remaining ounces out of an already-opened, mostly empty can. Then the FA opened a new can to top off the cup.

1B ordered Coke. Again, FA pulled out a pre-opened can of Coke.

Is this normal? How long ago could these cans have been opened?