Here at Mann Co., we take care of our mercs. After you’ve completed your first mission, you will get, free of charge, one Mann Co.-brand canteen. It's equippable in your action slot and filled to the damn brim with life-giving air. If air’s not your thing, these canteens can also be filled with a variety of power-ups at an Upgrade Station.
The Power Up Canteen is a default action item used in the Mann vs. Machine game mode. It is an empty brownish-beige canister similar to a drinking canteen, worn on the belt or back and additionally adorned according to the power-up that it's "filled" with. This item was originally obtained by completing your first Mann vs. Machine mission or via the crafting system.
When equipped and filled at an Upgrade Station, it is valid for up to three uses. Using the Canteen will alert the entire team via a sound cue as well as a message in the chat box. If it is not equipped, a notification will be displayed allowing you to equip it by pressing J or cancel by pressing K. The notification will continue to be displayed until you equip it, as long as you are on a Mann vs. Machine map.
The Power Up Canteen also doubles as a cosmetic item, showing up on the class model's belt.
Medics have the option of giving their Medi Gun the "Canteen Specialist" upgrade, which applies the effects of any Canteen the Medic uses to the player they are healing. The effect is instant and only applies to the one teammate being healed upon usage; boosts of timed duration cannot be shared across multiple teammates like ÜberCharges can. The Canteen Specialist upgrade also reduces the cost of refills for the Medic by 10 per level (with a minimum of 5) and increases the duration of any timed effects by one second per level.
There are currently 5 buff types. You can only fill one canteen with the same buff, each with up to 3 uses. After being filled, the canteen changes its appearance, though they all glow.
||Supplies 5 seconds of ÜberCharge to user and a Wrangler shield that blocks 90% of damage to their Sentry Gun.
||Critical Hit Boost
||Full critical hits for 5 seconds. Triples firing rate of user's Sentry Gun for 5 seconds.
||Ammo and Clip Refill
||Instant ammo and clip refill. Also refills Metal and Sapper; does not refill Sentry Gun ammo or Cloak.
||Teleport to Spawn
||Immediately returns user to the respawn room and supplies a temporary speed boost. Cannot be shared by Medics.
||Upgrades user's buildings to Level 3 and fully repairs all existing buildings almost instantly. Only available to Engineers.
||Ghost in the Machine|
Use a canteen charged with 'Teleport to Spawn' and then kill the bomb carrier within 5 seconds.
During a wave, use a canteen charged with 'Instant Building Upgrade' to build a new sentry gun within 3 seconds of your previous sentry gun's destruction.
As a Medic, share your canteen 5 times in a single wave.
During a wave, use a canteen charged with 'Ammo Reload' to refill an empty weapon slot.
August 15, 2012 Patch (Mann vs. Machine Update)
- [Undocumented] Added Power Up Canteen to the game.
April 3, 2013 Patch
- Fixed a bug in Mann Vs. Machine related to carrying buildings and using the "Building Upgrade" canteen.
November 6, 2013 Patch
- [Undocumented] Fixed the bug that made the Battery Canteens and Power Up Canteen unusable.
February 29, 2016 Patch
- [Undocumented] Added a normal quality Power Up Canteen as a default action item.
- Backpack icons for each buff type exists in the game files. These backpack icons shows a different texture comparing to the final ones:
- The Übercharge buff canteen has a cross icon instead of an Übercharge icon.
- The Critical Hit Boost buff canteen has a lightning bolt icon instead of a Kritz icon.
- The Ammo and Clip Refill buff canteen is darker.
- The Teleport to Spawn buff canteen has two arrows as an icon instead of a house icon.
- The Building Upgrade buff canteen has a different color.
- On one of the update pages there is a torn photo next to the canteens, indicating that there may have been a sixth upgrade.
- Two unused canteen types exist in source game files. Their internal names are RADIUS_STEALTH and SEE_CASH_THROUGH_WALL, and the actual effect of them is unknown.
- An alternative canteen price formula with Canteen Specialist upgrade purchased exists in source game files. The price would be decreased on 10 percents from original value per every upgrade tick, and the minimum price would be 1 credit. 
- Using a Building Upgrade Canteen while hauling a building results in the building retaining its current health and max health but will still upgrade the building to level 3 if possible.
- If the building is a Sentry Gun it will retain its current ammo counts, but will still receive a full supply of rockets if going from level 1 or 2 to level 3.
- If the building is a Dispenser it will retain its current metal amount.
- If the building is a Teleporter and the other end of the Teleporter is already placed, then the Teleporter being carried will have its max health be based on the placed Teleporter, but will still retain the health it had when it was picked up. If the other end is not placed it will act like the other buildings and keep its current max health, however placing the other end will not update the max health to the correct amount and both ends will be stuck with the max health the Teleporter had before being picked up.
- Abnormal maximum health (such as a level 3 building with 150 max health), can only be removed by destroying the building or purchasing a building health upgrade.
- The Ammo Refill Canteen suffers from several bugs.
- Activating 'MMPH' with the Phlogistinator as soon the Übercharge Canteen is about to run out will cause the invulnerability effects of the 'MMPH' to end mid-taunt.
- If a Sentry Gun has the Wrangler shield active when the owner uses an Übercharge canteen, the Sentry Gun will not gain the 90% damage resistance shield and instead keep the normal Wrangler shield.
- Crit canteens say they double your sentry firing speed in-game, however because of rounding, the canteen will actually triple a Sentry Gun's base firing speed. If the user has purchased a firing speed upgrade, or is using the Wrangler, then the firing speed will be doubled as claimed.
Unused Übercharge buff canteen backpack icon
Unused Critical Hit Boost buff canteen backpack icon
Unused Ammo and Clip Refill buff canteen backpack icon
Unused Teleport to Spawn buff canteen backpack icon
Unused Building Upgrade buff canteen backpack icon