Rain water in passanger floor

classiic HVAC failure? LHD left hand drive car , no country told.
own for how long, 2years or 1day/ or what ( right passenger door?) for rain. ingress.
you said water, well that can be clean pure water
from RAIN or HVAC evap condensate,
using AC cool or heat + defrost mode? or just pure heat mode?
I do not know what you do there
i tray to capture water,in jar,and see if it is green or yellow or pink
that is AF antifreeze,
and put my fingers in it and rub fingers to thumb and it feels very very slippery, that is AF. not water
if i sniff it and smells sweet it is AF>
(3 ways to discover AF antifreeze)
ok it's water, so dont use AC or Defrost mode.
so that be RAIN or defrost condensart
sorry i could never even guess the water gravity effects from any car made from fire wall to rear of care, gee hills even change that.
learn to do deeper inspection of all carpets there.

bad door gasket
or last drove car with say a bandanna hanging out the door.
a 1 time event,nobody can guess ever.
and allowed rain to go inside any car.
or windows were not fully up.

So you're saying you replaced the heater core because water was puddling on the driver's side, but water is still puddling on the driver's side? I'm assuming you're in the US and the driver's side is on the left and the heater core is on the right side.
Do you get much rain where you live? Is the vehicle parked outside? Do you notice the puddling more often after a rain? If this is the case, your water intrusion may be because of a leaking seal around the windshield or door. Check by getting the floor reasonably dry, and then have someone sit inside while another floods your car with a garden hose - specifically the windshield and driver's door. Have the inside observer try to catch a stream of water along the edge of the windshield, along the door jam, or along the door sill.

Check for leafs that are blocking drain holes on both ends . Air inlet cowl in front of wind shield. This blockage would cause water to back up and enter the Hvac air inlet.

Have you checked the rubber door seals for ingress?

Hole in firewall rain leakin down and in. At least thats my prob. Some silicone should work

the water is draining from the windsheild area there is a drain and that drain has become blocked with dirt or leaves etc

It is most likely coming from a dried up or improperly installed window seal at the bottom of the windshield (under the wiper trim)

Take the trim off and caulk yourself - or have the entire seal replaced.

Thanks for using FixYa - a FixYa rating is appreciated for answering your FREE question.

when whe got our 1999 chevy caviler ours done that to around the windows on the left side. we ended up hafing to replace the seals around the left side windows the wondsheild and back windo.

sounds like a plug is missing
or the drain in front of the wind shield is clogged

Go to a car wash with a good flashlight, and watch where the water comes from.