I HAVE WATER IN THE BOOT OF MONDEO VERONA 2000 1600CC?

I HAVE WATER COMING INTO THE BOOT OF MY CAR, i ONCE HAD THE BACK REAR LIGHT SILICONED AS SOMEONE ELSE ON SITE HAS SAME PROBLEM, BUT i CAN'T BE SURE IF THAT'S THE ANSWER AS IT'S SOAKING WET AND RUN INTO REAR SEATS.
ALSO IT GETS VERY DAMP IN MY CAR ON BACK SEAT FOOTWELLS?
PLEASE HELP IT'S DRIVING ME LITERALLY ROUND THE BEND!!