2007 hatchback 1.5: Puddle in rear driver-side footwell

Hey everyone,

This morning I drove my 2007 Prius for the first time in 16 days. I drove it for about an hour.

When I got home, I saw this in the rear driver-side (right-hand) footwell:





It was not raining while I was driving. I keep the car parked on the street, and my region has had the rainiest September in recorded history, and we have had multiple yellow alerts for rain in the past week.

It's possible that the puddle was there when I set out, and I just didn't see it. I throw my handbag back there while I'm driving, and I only noticed it when I went to pick up the bag. That is also how I know the puddle was not there the last time I drove the car.

I called up a body shop that I trust. They previously have saved me from puddles in the passenger footwell by noticing that a plug was missing, so I thought they might be able to help this time. But they said it was beyond their expertise.

I called up my usual garage and will take it to them tomorrow. However, they don't specialize in this kind of thing. So I thought I should ask here. I see that some people have had comparable experiences, but without any definitive answers that I could find.

Has anyone experienced something like this? Did you find the source of the leak?