Passenger floor wet on s60 volvo 2002?

Sounds like a leaking heater core or faulty hose connections.
Sniff a tissue after blotting some of the wetness or; it may not sound appetizing, but to check if it is coolant + water, take a clean cloth, blot the wet spot and touch the other side of the cloth to your tongue.
Coolant doesn't have a strong odor unless it is hot but it lends a sweetness to the coolant that is easy to detect. That is why one shouldn't dump coolant on the ground since domestic animals will lap it up.