Can we buy duty free and bottles of water to take on the plane or will the 100ml liquid restriction also be in place at TSA?
yes you can I travelled from Dublin to California with Aer Lingus on June 17 2018. I bought alcohol in duty free, which they sealed in a plastic bag, I also bought water and organge juice. For the second secirity clearance you take off your shoes and take out electronic equipment.
About 2 hours before my flight departure time, an announcement was made for my flight , that passengers should proceed to the USA Pre Clearance Area.
This is a special arrangement that airports in Ireland have with USA Homeland Security. It means that USA Homeland security have a station in Irish airports and non USA Passport Holders get their stamps in their passport IN IRELAND BEFORE BOARDING THE PLANE.
To go to this special security area, you leave the general shopping concourse and go down to the departure gates. You then follow the signs to the lower level and to the security check.
At this second security check, you need to show your passport and Boarding pass. You then go through another bag check, where you remove your shoes and electronic items.
Once through the bag check, USA passport holders go to the self service machines, and non USA passport holders go to the USA Homelands Security Agents. This is where they ask you the questions about your travel plans, and put the stamp in your passport.
Once through this security check you are technically in America, even though you have not boarded the plane.
After this security check is where the USA boarding gates are. In this area there are limited shops, and food options, so you need to make sure you do your main shopping before going through the USA Security.