You mean water from spark plug on the left side of engine drains through this hole on the right side ?
Singh JI, all the UCE engine have only one water drain on the RH side weather its domestic or export C5.
The one and only primary plug you have does not have a drain hole like on RH side. There is a gap between the fins and the block near the LH side head bolt(next to primary plug) Water does not collect there.
While on Rh side where there is a secondary plug or in export models just a deep cavity. On RH side the fins have metal to metal contact with the head without any gap(Rh side of head is wider then LH side) so they have intentionally had a drain hole because of the cavity form due to the head design.
The oil/moisture you see is from the barrel /head gasket. Tighten the head or replace the metal gasket if you dont want to see any oil there.