Wet feet and SAM unit failure are common results of water ingress through the Roadster bulkhead. Sadly, this is one of the many points where the Roadster leaks. There are many preventative methods publicised, some more drastic than others. One method involves sealing any joints between the various trays that sit beneath the scuttle. The following pictures show a right-hand-drive Roadster. If yours is left-hand-drive, then mirror the images.

In this guide, the bonnet, scuttle and wiper motor have all been removed.

As you face the car, the wiper motor tray is on the left with the internal air duct on the right. As the interior fan is turned on, the flow of air is across the wiper motor and into the air duct (shown in blue).

The wiper tray has a shallow fall to a low point, indicated below.

There is a very small drain hole at the low point allowing any rainwater, falling through the vents in the scuttle, to drain away.

It is not uncommon for leaves to get drawn into this tray by the flow of air to the internal air duct. If this drain gets blocked, rain water will fill up the tray and overflow into the driver's side footwell. It will also soak into your wiper motor, leading to possible failure. Therefore, it is worth checking this drain from time to time by looking through the vents in the scuttle. If you can see any debris, clean the tray as much as you can.

The drain is connected to the grey downpipe shown below. This is made out of rubber so check that it isn't blocked by squeezing it down its length. Also check that the pipe drops through the undertray.

If you are still not confident, you can try sealing the joint between the wiper motor tray and the car with sealant as follows:

For the air intake, you will notice that the actual duct has a gulley around it. This is to prevent any water from getting sucked down into the interior fan. Most of the water will fall down the gulley and drain away. Again, the blue arrow shows the direction of air flow.

Looking inside the duct, you will notice that there is a foam seal between the duct/gulley assembly and the rest of the car (arrowed). This isn't the best form of seal and you will need to reinforce this with proper sealant if you are experiencing water leaks in the passenger footwell. At the bottom of the duct, you will see a drain point.

Although it is highly unlikely to find leaves obstructing this drain, it is still worth checking to see that is isn't blocked. The drain exits into the bonnet bay.