Last week the secondary screening was mainly to find liquids and not allow them on the plane - even water bottles that were not empty. Not sure why - apparently their initial screening at the entry to the secure area is not adequate.
It is because the secondary screening is necessary only for flights departing for US and Australia. It is ok to carry water bottles on board if they are bought after clearing the security and the destination is not these two countries. However, for US/OZ bound flights, all liquid containers >100 mL will be confiscated, even thought they are brought within the secured area or taken from the lounge.