We generally use sturdy, reusable/refillable 5 gallon bottles for our water cooler but sometimes we get disposable ones (usually when we didn't time it right and the refill place is closed, or like in this case, their refill station is frozen.) The disposable bottles are thinner, flimsier and always collapse on themselves slowly as they empty, as you can see in the photo.

So clever me figured I would try to get it to not collapse by poking a little vent hole above the water line. Makes sense no? A vent hole. Like a coffee cup. But instead of expanding the bottle, it actually made the water cooler leak uncontrollably. Or flow freely… you know… like a coffee cup? 😄

So I turned to a LLM for an explanation. Here's what it had to say:

Two really interesting bits of physics and design are happening in your water cooler, and they fit together more tightly than most people realize.

Why the bottle slowly crushes as it empties A 5‑gallon water jug on a cooler is not vented to the atmosphere. When you flip the bottle upside‑down and place it on the cooler:

• Water flows out of the bottle into the reservoir.
• Air cannot flow back in, because the neck of the bottle is submerged inside the cooler’s internal water tank.
• As water leaves the bottle, the air pressure inside the bottle drops.
• Outside air pressure (much higher) pushes inward on the thin plastic walls.
• Result: the bottle slowly collapses or “crushes” as it empties.
• This is exactly the same reason a sealed plastic bottle dents inward when you suck the air out or cool it down.

The crushing is normal and expected. It’s part of how the cooler regulates flow.

Why poking a hole made the cooler leak When you added a hole above the water line, you unintentionally broke the pressure‑based flow control system.

• Here’s what normally happens in a properly sealed bottle:

• The cooler only lets water out when the reservoir level drops.

• As water leaves, a small bubble of air glugs up into the bottle.

• That bubble equalizes pressure just enough to let more water out, but only when needed.

• The nozzle doesn’t leak because the reservoir stays at a controlled level.

But when you poke a hole:

• Air can freely enter the bottle at all times.

• The bottle is no longer sealed, so there’s no vacuum to hold the water back.

• Water flows continuously out of the bottle into the cooler’s reservoir.

• The reservoir overfills.

• Once overfilled, water escapes through the nozzle or drip tray.

In other words: The hole turned your cooler into a gravity-fed open tank, so it overflowed.