Vauxhall Tigra water leak

There is a water leak and it soaks the floor on the back behind the passenger side. I have searched but no water coming in at doors or windows, the only place i can think it is coming from is the boot. There is a little bit with holes for the water to drain and a pipe that i think might be disconnected somewhere in there. Any ideas. I have sucked the water out with Vax hoover and tried to dry it but it still seems to fill up. Also there was a little plughole just under that place and the plug was lost so i got one in but this is making it worse. Maybe i should remove that again to let the water out. Help!!!!!!!