For decades, I've been using either Rain-X or more recently, AquaPel on my windshield. It causes light rain to bead up rather than spread out which, I think, makes the sensor more likely to turn on and wipe. Depending on your speed and the wind, you may not need the wipers at all, since it can just be blown off. Some people love the stuff, some hate it, but from a safety viewpoint, I find it quite handy, especially on a wet, slushy winter day...getting a windshield full of slush, you can still see, whereas, normally, you'd have to rush to turn the wipers on. Even though I've had my i3 over a year, I really haven't been out driving all that much in the rain, but my thoughts are that it is a little slow to respond, but, you can adjust that somewhat with the control on the stalk, if I remember correctly. Check the manual to confirm.