2001 Volvo V70 with sun roof...car sitting in heavy rain..return to car both front drivers side and passenger side footwells were full of water. What could cause this..no the windows were not open or the sun roof.

Once you have checked it isn't a car window that is slightly open there is three main reason for water in the foot wells. Sun roof, door seals and heater matrix.
If you have a sun roof fitted, check it is closed correctly. Open it all the way and check the running grooves it sits in for dirt and blockages. There are drain holes in the runners so try cleaning the runner grooves with an old toothbrush.
Open the front door on that side of the vehicle. Take a good look at the rubber seal the door presses against when it is closed. Any damage or splits can create leaks into the vehicle. Check the rear door seal for the same thing. If you can, check all the other door seals and the trunk/boot seal as well. These seals are usually a tight fitting 'push on' type which you can replace yourself.
This will sound silly but does the 'water' smell of anything? The heater matrix is under dashboard and is what supplies the heat to the heater blower controls on the dashboard. If this is leaking the leak will have a sweet smell as this is coolant from the engine. This is a big repair as you often have to remove the whole dash to repair it.

A simple test is to feel around the carpet in that footwell. See how far up under the dash the carpet is wet. Does it only happen after rain? Do you have a sun roof fitted?
If the carpet is only wet low down on the floor the most likely reason is either a perished or damaged door seal rubber, a faulty sun roof seal or the drain channels for the sun roof are clogged up. Check the footwell in the back as water always flows and settles at the lowest point in the vehicle.
If it is high up and nearest the middle of the dash you issue could be the heater matrix under the dash but as it seems to be only on one side this might not be the issue.
Door seals are a simple case of pull the old one off and push the new one on and they don't cost silly money to buy. Heater matrix issues, unfortunately, usually involve taking the whole dashboard out to get to it.
Hope this helps.

And where exactly is this rain coming from? The sun roof? The door seals? Seeping in down in the footwells (soggy carpet)?

Sometimes "rain" can be mistaken for A/C condensate that is not draining due to a plugged condensate drain. If your A/C is running and it's hot and humid out then you should see some water drips on the ground underneath the front area of the vehicle. Let it sit in one location for a few minutes after you come in from driving it. Let it sit for a few minutes with the engine and A/C running. Move the vehicle and look for the telltale wet spots from the condensate drain. If you don't see a wet spot then chances are the drain is plugged. The condensate will back up and drain inside the car ...typically in the passenger footwell and making the carpet wet.

Sun roof ¿
wiper motor compartment
full of leaves
rust issues
door seals?

try underneath car normally plastic drain plugs ,if one missing water can get in that way

so if i were you i would be checking drain plug or drain opening in front of wind shield. probably it is under plastic grill next to wipers. it transfers the collected rain water infront of windshield and direct it to ground. if it is clogged flooded water can drain into cabin.

If you have a sun roof,the drain hose may be off. If so,remove the sun visor and pull down the head liner, to get to the hose and drain fitting on the sun roof opening

you have 2 drains in the front that go down the a pillars and dump near the fenders.

The rear usually go down the B pillar or C pillar and out thebottom near the rocker panel.

Blow them out from the top with compressed air and make sure you have air flow at the exits.. Open the roof to see drain holes in the four corners.

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• The roof opening panel leaks

• Roof opening panel adjustment.
• Front rail seal.
• Drain tube attachment points.
• Roof opening panel water trough and seal.
• Roof opening panel drain hose.
• Roof opening panel seal.
• Roof opening panel.

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1 is the drain hoses

The sunroof drainage gets blocked.

your footwells will fill with water - even under your seats right to the back seats footwells

See two 10mm holes in front sides when sunroof is open.
a) push a flexible cable down from the top - it comes out just behind the front wheels. (use electric three core cable - or TV aerial cable - a hanger is too short) - you need about a metre and a half)
b) remove the inner mudgaurd behind the front wheels (2 screws) you will see the end of the plastic drainage pipes - remove the blocked black rubber cup at the end of these - why they are there is anybody's guess)