leaky hatch

there is a leak in the seal on my hatch and there are 2 inches of water in the bottom of my hatch.It sucks and everytime it rains more water gets in.so how can I find out where the leak is and how could I fix it.

sit inside the hatch and tell a friend to hose down ur car and try to see where the leek is coming, surely is from any worn out ruber or maybe rusted out part.

thanks