The 3.4 Ounces (100 mL) Rule: TSA's Liquid Restrictions When it comes to bottled water, this rule means you can't bring a full water bottle through TSA security checkpoints. This may seem like an inconvenience, but it's a rule put in place to ensure air travel safety.

According to current TSA regulations, there is no limit on the physical size of a water bottle you can bring through security, but there is a strict limit on the liquid content. Under the "3-1-1" rule, your bottle must be completely empty when you present it at the security checkpoint. Once you have cleared the X-ray machines and body scanners, you are free to refill your bottle at any water fountain or hydration station within the secure terminal area. If you wish to bring a full bottle of water through security, it must be 3.4 ounces (100 milliliters) or less and fit inside your single, quart-sized clear plastic bag of liquids. The only major exceptions to this rule are for "medically necessary" liquids (such as distilled water for a CPAP machine) or for "infant and child nourishments" (like baby formula or breast milk), which must be declared to the officer for separate screening. For 2026 travel, the most efficient strategy remains bringing a sturdy, empty reusable bottle—like a Hydro Flask or Nalgene—to avoid the high cost of bottled water inside the terminal while staying hydrated throughout your journey.