Suggestions please.

Have just discovered that my wifes 02 Reg Passat sedan has a leak leading to water filling up the little storage compartment on the RHS of the boot (opposite the compartment used to store the jack, etc). Rest of the boot seems bone dry, just filling up the storage compartment. The family has had plenty of these cars over the past 15 years, so I'm quite used to dealing with water leaks at the front of the car, this however is a new one to me.

Anybody had a similar issue?