It appears that having a Safari snorkel is not a guarantee that you can go paddling in safety - witness the D3 I saw at ULR about a month ago with the body off (to remove the drowned engine). It looked as if the snorkel had leaked where it joins the Land Rover air box - possibly a poor installation but worth bearing in mind whatever you choose....check the installation!
I spoke to people both at Land Rover Experience and the factory last year and their view was that provided it was sealed to the body, it was perfectly adequate - if you keep to the wading limits...
Hope that doesn't add too much confusion....

