| Had just come off a 12-hour flight from Hong Kong and had to connect to get a domestic flight. We arrived at Terminal 5 but we were at the C Gates, so we were required to travel to the main terminal by train. It was around 5 in the morning and at least 2 flights had landed with a large number of passengers. There was only one train available that needed to take people back to the main terminals before returning to the C Gates and back and forth, so this took longer than expected. We were then required to go through security again however there were no signs or guides advising that we needed to do this. In some other international airports that we have connected, there is no need to go through security checks again. Because we only had 2 hours to connect, we decided we would try and head straight over to our gate before going to the toilets etc., but we encountered security instead. The queues were all over the place and you could see everyone was a bit fed up at this point. I had just come off the plane with at least 500ml of water left as well and instead of being helpful, I was shouted at for having a large bottle of water and was told to empty it on the spot by drinking it all (seriously?) or the security guard would bin my water bottle (was desperate for the toilet as well at this point). When we told her that nobody informed us that there would be security checks again, she shrugged and told us we should've emptied it in the toilets - obviously, I would've done that if I knew we had to go through this again! Overall she was incredibly rude, treated us as if we were stupid, put the blame on us and made our experience absolutely awful. If I had gotten her name I would've made a formal complaint. Honestly the worst airport I have ever experienced and would avoid in the future if possible.