Beer glasses are obtained by drinking certain beverages (such as beer), from the shelves in the Sorceress's house or from a kitchen shelf (Wooden shelves 2 or higher) of a player-owned house. They can also be made with molten glass using the Crafting skill.
The beer glasses obtained from a player-owned house are a separate item from standard beer glasses. As such, the two cannot be used interchangeably with one another. For instance, a standard beer glass cannot be used to obtain beer from a beer barrel in a player-owned house; likewise, player-owned house beer glasses cannot be used to obtain beer from a Calquat keg. In addition, player-owned house beer glasses cannot be taken out of player-owned houses, as they will simply vanish.
Also, if you find a barrel with a small spout protruding from it with examine text of "The barrel is full of ale" or "Mmm...beer!" you can use a beer glass on the barrel and fill the glass with beer. However, if players do this with the ale barrels in the pub in Gunnarsgrunn, the barbarians will turn protective of their beer and attack the player. Currently, the only barrel F2P players can successfully obtain beer from is located on the docking piers at Musa Point.