Get inside with a flash light and a friend outside with a garden hose and find out where the leak is.
There is obviously a leak in either the firewall/cowl area or the window seal.
Water can get in when the firewall flashing is missing outside under the windshield cowling. The water gets into the heater/defroster system and then drains on to the floor.
There is a drain for the air conditioner condenser located under the hood on the firewall. This often gets plugged (by dirt,leaves etc.) This allows water to back up into passenger compartment often soaking carpet.
Rain , because when it rains all the water gathers until it spreads around to other areas.
Since it happens only when it rains, it would suggest a few possibilities. Look for these:Bad window or door seals.Bad windshield seal.Holes in the floorboard or firewall, especially near the wheelwells.
Have someone inside the car while you spray it with a garden hose. Start from the bottom and work your way up until you find it. I don't know what area the water leak is coming from....upper or lower....but you may have to pop the hood and spray around the firewall also.
First you have to find where the water is coming in. Have a friend use a water hose around the windshield, cowling, etc. while you check inside for leaks. Water could be coming through the firewall around gaskets as well. Be careful to not soak any electrical components if squirting water under the hood. After finding the leak then you can decide the best course of action to stop it.
Leaky weatherstripping around the doors.
Check AC drain and clear the blockage. Also look for firewall sealer skips.
sounds like there could be a plug knocked out of the firewall on the passengers side which would allow water to enter when you hit some puddles and splashed up
they get water when it rains
A great example of weathering would be the Grand Canyon. The Grand Canyon is partially made by the rivers running throughout the valleys. Another example is when it rains water falls into cracks of rock. If it gets cold enough to freeze water then the water will freeze up and the rock will break.