TSA Allows Frozen Liquids Only if they Are Frozen Solid
TSA allows frozen liquids if and only if they are presented frozen solid to security checks. This is in my opinion a fairly sneaky way to say
good luck with that seeing as freezing water at room temperature requires a fair amount of pressure to be applied on it. You can always try to find a liquid that presents itself in solid state at room temperature, and try to bring that through security.
ice on the TSA prohibited item search tool yields the following result:
Search Results For: ice
! Special Instructions
Frozen liquid items are allowed through the checkpoint as long as they are frozen solid when presented for screening. If frozen liquid items are partially melted, slushy, or have any liquid at the bottom of the container, they must meet 3-1-1 liquids requirements.
If the frozen item is packed with ice or ice packs in a cooler or other container, the ice or ice packs must be completely frozen when brought through screening. If the ice or ice packs are partially melted and have any liquid at the bottom of the container, they will not be permitted.
Medically necessary liquids may be accompanied by ice packs, but we ask that you declare these items to a security officer for inspection.
You can pack frozen perishables in your carry-on or checked baggage in dry ice. The FAA limits you to five pounds of dry ice that is properly packaged (the package is vented).
The 3-1-1 rule for liquids, aerosols and gels in carry-ons is as follows: containers must be 3.4 ounces or less; stored in a 1 quart/liter zip-top bag; 1 zip-top bag per person. Larger amounts of non-medicinal liquids, gels, and aerosols must be placed in checked baggage.
If the liquid is considered a hazardous material that is permitted onboard an aircraft, it is still subject to the 3-1-1 limitations. Many questions arise on whether an item is hazardous material and what requirements must be met to take it on an aircraft. The Pipeline Hazardous Material Safety Administration (PHMSA) at 1-800-467-4922 or the aircraft operator on which you are flying can assist you with your questions concerning hazardous material.
Even if an item is generally permitted, it may be subject to additional screening or not allowed through the checkpoint if it triggers an alarm during the screening process, appears to have been tampered with, or poses other security concerns. The final decision rests with TSA on whether to allow any items on the plane.