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Editor’s note: This post was updated with new information.

Full-size liquids are among the items travelers most frequently forget to remove from their belongings before passing through U.S. airport security — the Transportation Security Administration’s 3-1-1 liquid rule prohibits travelers from carrying liquids, specifically gels, aerosols and spreadables larger than 3.4 ounces.

Of course, you can bring an empty water bottle to the airport to refill at a fountain once you pass through security, but if you want to bring a beverage from home to enjoy on the plane, there’s one more solution.

Per the TSA rules, travelers can bring frozen liquids through security, specifically those that are “frozen solid when presented for screening.”

Items that are “partially melted, slushy or have any liquid at the bottom of the container” must meet the standard 3-1-1 liquids requirements.

An exception to this rule is breast milk, which is allowed in carry-on baggage in quantities greater than 3.4 ounces. This can be helpful for nursing mothers, as the TSA permits milk, formula and pumped breast milk through security without set limits because it treats them as “medically necessary liquids.”

According to the TSA, “Formula, breast milk, toddler drinks and baby/toddler food (to include puree pouches) in quantities greater than 3.4 ounces or 100 milliliters are allowed in carry-on baggage and do not need to fit within a quart-sized bag. This also applies to breast milk and formula cooling accessories, such as ice packs, freezer packs and gel packs (regardless of presence of breast milk). Your child or infant does not need to be present or traveling with you to bring breast milk, formula and/or related supplies.”

Regarding how much you can bring, the TSA specifies “reasonable quantities.” Summer Hull, a director of content at TPG, notes that this leaves some discretion up to the individual officer.

In her experience, there’s an unwritten cutoff when your kids appear to be 2 or 3 years old. At that point, the TSA tends to stop allowing families to bring other liquids through security, even if it’s a drink for a kid in your group. To avoid any liquid for your child getting tossed, she suggests the frozen method as a workaround.

“While the TSA rules permit frozen liquids going through security, and I can vouch that it does usually work in practice, some TSA agents simply interpret things differently from most, so be prepared with the rules if you don’t want to toss your drink,” she said. “I also wouldn’t [bring] a dozen different frozen drinks unless you are looking to land yourself in some secondary screening.”

Related reading:

• What not to pack in your carry-on bag
• Your guide to flying with kids of every age
• 42 real-world family travel tips that actually work
• TSA to pilot self-service security screening in Las Vegas