if there is a fault in the cooling system it wont matter if its water, coolant or concentrate in there.. it will still over heat. water will have a higher boiling point the higher the pressure is in the system. having coolant in there will raise that by a few degrees if that.
as for water pump.. if you read further up he said he's been tracking it for ages and this has only recently become a problem. besides theres plenty of other RB20's that get tracked and thrashed at high RPM with no issue.. the pump is not the fault here.