Has your scuttle got any cracks in it? If so replace. Also check the bonnet release gromit and around the blower fan intake if these dont seal right then water can seep in. Just chuck a big blob o' grease all over em and see if that helps. Have a look in the scuttle area and make sure all the rubber blanking gromits are in place and sealed properly too.
Another thing, are you sure thats where the water is coming in? Its common for water to leak in through the front windscreen seal, worth checking that too.