Don’t treat what is already clean and don’t mix clean water with dirty as it will increase the volume of dirty water.

Condense water from the main engine air cooler, air condition drains etc. is normally very clean and the IBTS ( Integrated Bilge Water Treatment System) as per Marpol MEPC.1/Circ.642 recommends discharging it directly overboard without monitoring it. However  oil can be present if something goes wrong and will not release the crew from responsibility even though it is a Marpol sanctioned design.