Helsinki has drinking water fountians.
This is from the http://www.finavia.fi website about Helsinki
“A total of 12 washrooms in our main traffic areas now have cold water taps where passengers can refill their empty water bottles with cold drinking water free of charge. These automatic taps are located in 6 men’s washrooms and 6 ladies’ washrooms found near Gates 12–13, 21, 26, 29 and 32,” says Jukka Isomäki, Director at Finavia.
In Finland, all tap water is pure, fresh and drinkable all over the country. Finland’s tap water ranks among the best in the world, according to the United Nations.
Or you can buy a bottle of water for 1 euro