laguna water leak?

Hi again i have a 1.8 laguna rt, its started using water within the last week, lots of water, anyway, how can i best find where its leaking, carpets are dry, no emulsification of oil just the same colour it was before, and i cant see any water coming from hose connections, i was thinking of bunging in radweld or similar but as the heater matrix was replaced winter 2004 im pretty loathe to do this in case it blocks again, any ideas or suggestions appreciated guys
Paul