Can drinking a diet soda make you gain weight or lose muscle even if you are drinking plenty of water? This is a pretty simple answer.
If the soda gives you more calories then you need:
If the soda doesn’t:
No (diet sodas are less to 0 calories)
Regardless, you don’t want to flood your body with sugar or sugar substitutes. Limit your intake. Keep yourself hydrated. And drinking sodas won’t make you lose muscle.