If you have just one or two drinks it will help a lot, otherwise it will be more difficult to make friends with your flatmates (or not, you might be put in a non drinking flat if the uni gives that option). Fresher's is mostly about bonding, and that generally happens via alcohol so it will take a bit longer to get to know your flatmates or they may form a clique before you get the chance.
That said your University may offer non-drinking events during fresher's which could act as somewhat of a replacement, not to the extent of flatmates but something.