Hi, i have a 2017 Mazda 3 sport nav saloon and recently there has been water getting inside the boot. It seems to mainly be at its worst on the left side as pictured below. All the body work and cables/connections at height are bone dry, along with areas around the light clusters etc. The rear seats which i folded down are completely dry at the rear. There is signs of some drops of water to the rear of the boot just before the rear of the back seats start, but these are only very small. The worst of it is a puddle to the bottom left as pictured. The well of the boot also had a puddle. The right hand side wasn't as bad with only a few signs of water. I have checked the boot seal and the light cluster seals, all bone dry from within. Also the lip of the boot is bone dry also with no signs of water. There is a slight rust patch half way up as pictured, which kind of says to me that's where the worst of it is getting in but I'm not sure. This happened whilst the car had been parked up and hadn't moved. Any advice would be great!

 

I think that the water we see in the pictures is the water that remained because it is at the bottom and that is understandable.
You can't see the moisture on the cables and on the sides of the trunk because the water quickly drains down, to the bottom.
It might help if you put paper towels on the sides and tape them to the side sheets.
Wait for the coming rain and you will see a path where the water flows from the top to the bottom.