Vault 13 Canteen

"You've taken a sip from your trusty Vault 13 canteen."

 is a miscellaneous item in Fallout: New Vegas.

Characteristics
The canteen essentially stores an infinite source of water, automatically lowering the player's H2O meter on a regular basis, and is useful primarily to ward off dehydration in hardcore mode, as well as restore a very small amount of health, even when not in hardcore mode. The canteen can also help with the Achievement/Trophy "Hardcore".

In both hardcore and casual mode, as long as the canteen is in the player's inventory, the player will periodically receive a message at the top left corner, "You take a sip from your trusty Vault 13 canteen", and the H2O meter will drop. Since H2O is not important in casual, non-hardcore mode, this may become more annoying than useful.

The canteen seems to trigger the player's drink and subsequent notification when the H2O meter reaches a certain level (something just under 200 where dehydration would set in). However, under certain circumstances - such as sleeping or fast travelling right before the hydration level reaches the trigger point - the player can "jump past" the trigger point and become dehydrated.

There is no way to deliberately force a drink from the canteen. It only works as an automatic hydration source.

There is no player animation associated with drinking from the canteen; the screen notice and H2O meter drop are the only indications it is working.

Location
The Vault 13 Canteen is acquired exclusively from the Classic Pack.