Are you sure it is plain water? Exactly the same thing happened to me a few years ago (on a different type of car), and it turned out to be a cooked heater matrix. I don't know how the cooling/heating system works on the clio, but one sure way to test is to check the level of coolant in the radiator. If it keeps needing topped up then it may be something to do with the above. You'd probbably smell it in the car if it was the above, though - engine coolant is generally quite a strong smell! This is just an idea, assuming it is not a leaky windscreen or something like that. I guess it could also be a damaged bulkhead seal somwhere. Probbably quite unlikely but perhaps worth checking. Some people who install these fancy sub woofer systems these days need to hard-wire direct on to the battery which means running wires thru the bulkhead. Depnding on how this was done could mean damaging or even removing a seal.
TEfLoN, June 2006