2008 XC70

As soon as I got my first water on the floor, I put duct tape (thin duct tape, not the stiff silver type) all around my sunroof. The next bad rain, I had an inch on each front floor.

It was then suggested that the windshield was the problem - I had a new one installed, still got a flood the next bad rain.

One symptom that I observed was a streak of water on the street when I took a left turn out of mu driveway. Does your car do this?

This suggests a problem in the cowl or the AC drain.

My dealer cleaned the sunroof drains three times - the last time the head mechanic did the job.

The flood is still gone, but the streak on the street remains.

I have another XC70 that does not leave a streak.

As Klaus suggests, there may be more water than you see. Check the subfloor under your car to see if there are plugs you can remove to drain more water. I got so angry that I was going to drill a few holes - a couple of holes that you could plug later would be better than a rotten floor.

https://www.volvo-forums.com/t36477-water-leaking-onto-drivers-side-floor.htm

First, check the drain in the sunroof. Pour a small amount of water into the left drain and see if pours on to the ground by the front wheel.

This is very common, be sure to remove the carpet and look under the padding to get another gallon.

And, if it happens on the driver's side, check the passenger side!
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Keeping it running is better than buying new

I'd start with making sure your moonroof drains are clear. Check to see if the headliner is wet near the sunroof/moonroof.

Don't know XC90's, but it wouldn't hurt to make sure the cowl area is clear of leaves and debris.

Also check the bottom of the door panels for wetness and check drains (if visible) at bottom of door.

Has your windshield ever been replaced? Sometimes they can leak down under the dash to the floor. Check windshield seal condition.