hiya mate .Normally when the floor is wet its coming from the front i suggest ytou check your windcreen bonding, firewall also the seals .If you have not worked on the car then i dont think it will be trhe floor as its rare for a floor pan to leak.Try the door seals and check by the passenger side seals ( Sorry your side drivers ) in the uk we say passengers side. Also what you could do is wash yuor car in dye ( food) and see where its coming from that works for people also it does not hurt damage your car as its bio so it is harmless.