Hello
The fact that the water is limited to the rear passenger side of the vehicle is a definate clue that the water is either entering around the door or from the trunk, yes that's right the trunk. Some vehicles that have a poor seal around the trunk will allow water to enter sliding off the back window. The water will run down off the back window, through the trunk lid and leak through the back seat and on to the floor. Rubber seals around doors and trunk lids need to be secured properly and aligned properly to the door opening to prevent water from getting in.
You described your problem well, thank's for mentioning that the water had no odor, that helped a lot. Wait for a dry day and get a garden hose and apply water all around the trunk lid and then around the door. Have someone stay in the car and look for any water that may leak in.
My goal is to save you money and time, I have a simple and logical approach for troubleshooting technical problems.
If you find my answer to be helpful, please remember to ACCEPT the Answer! Thank You!