Water leak on driver side.

It sounds like a leaking heater core. If your radiator level keeps loosing fluid? that will confirm this as the problem. The "Warm water" is engine coolant and is simply getting caught up in the lower dash board sloshing around as you turn
You probably need to replace the heater core . It is what gives you heat inside the car from the engine. Another symptom would be no heat inside the car caused by low fluid level. Driving too long like this WILL cause serious engine damage.

If the car is equipped with a sun roof the drains empty on either side down the pillars that anchors the front window.

In some cars the hose will fail or plug.

Hope thos helps

if this is a new shape meriva the problem is the wiper scuttle seal leaking water .it drips into the engine bay,onto the heater pipes and tracs into the cabin.Pour water onto the screen and look into the engine bay,just behind the engine and you will see it drip onto the heater pipes where they enter the bulkhead.It then tracs into the cabin and soaks the carpet.The problem is a foam seal on the scuttle panel when it should be a rubber one.One fix is to ensure that the seal where the heater pipes enter via the engine bay is dry and spray it and the pipes with underseal.Vauxhall are aware but dont have a solution?

Check the door rubber seal for flat spots or maybe something stuck to it causing water to get past it.

I recently purchased a 2008 BT50 dual cab then 2 days later we had 500mm of rain and of course it leaked :( I had about 80mm of water on the drivers side floor and 30mm on the passenger side floor. I stripped the interior out of the car and started hosing the outside and watching where it was coming in. I took all the windscreen surrounds off and the cowl panel off below the screen there was no water coming in from that area. I had taken the gutter seals off but left the door seals on so the water was running down around the outside of the seals (with the door shut) and out at the bottom. From inside near the drivers side kick panel I could see water coming through seams in the metal work and when I took the door seal rubber off the body on the car I could see water was getting in at the top of the door seal rubber going down the front inside edge of the rubber and getting in through the seam where the rubber push's onto the body of the car (first problem). I took all the door seal rubbers off and run a bead of non corrosive silicon inside the cavity and pushed them back on. It seemed to have fixed the problem I dried the carpet and put it back together..Two weeks later we got another 325mm of rain and it leaked again :( not near as bad this time. Looking at the bottom of the door where the door trim meets the door I could see water coming from behind the trim and then into the car. I took the door trims off and could see water gets in when the window is up (all cars do) and is supposed to run out the drain holes in the bottom of the door but the water was dripping and splashing up to the back side of the door trim against the sheet of plastic that is supposed to seal against the door with the black mastic (it doesn't) and running straight into the car. I cut some plastic and siliconed them onto each opening on the inside of the door frame and then put the factory piece of plastic on as well (properley this time) as a backup.
So far so good.

You could have a windshield that is leaking water. Often this water will trickle down from the bottom/inside of the glass and then down the firewall, under the carpet or floor mat, and to the floor. The way I usually hunt for these is to remove the floor mat or carpet then get a flashlight and lay down in the cab so you can see under the dash area while someone sprays water on the vehicle with a garden hose. Often the leak will show up as a trickle that you can then backtrack to it's source. Another spot to look for is at the cowl in front of the windshield where air for the heater and a/c is pulled into the passenger compartment. The water drain holes in this area can plug up and allow water to overflow into the passenger compartment. Good luck, hope this helps!

check the steering wheel boot or a hole in the floor pan

this vech was famous for the windshield leaking on the driver side lower part of windshield.. and the water drips onto the gem module and inside fuse panel and can cause may electrical problems.. a good way to tell is remove the 2 big connectors with a 10mm socket and inspect for any water in connector or where connector came from

Most likely water leak around windshield on the left side dripping down into the GEM module which is located on the back side of the interior fuse panel/