Just to add to what others said: in Barcelona, unless specifically stated as tap water (agua del grifo/ aigua de l'aixeta), if you ask/are offered just "water", it will be bottled water (and you will have to pay for it). The taste of tap water varies on different city areas, from bad to worse IMHO. It is very safe but very few people (including locals) drink it.
Most of we locals usually order both water and wine, so probably the waiters are willing to make sure you did not forget (plus trying to sell you bottled water of course). In any case, in this city, never assume that anything "offered" to you will be free.
Keep enjoying the city... and the weather, much better than expected! :-)