I've got two customers reporting white spots in a line down their windows. Caused by water running off the frame which for some reason is contaminated and hence drying as spots. I've been to inspect both houses after the windows have dried. And I've tried spacing out three glass only rinses as much as you can to solve the problem. To no avail. Both windows are wood effect brown uPVC. It's a trend I have in fact noticed with brown woof effect uPVC windows many times in the past. I find it hit or miss whether they will work with WFP. When I take on a new customer with these windows I give it a try with the WFP and if it doesn't work I just trad it. However, on these two I'm reluctant to trad it as both jobs involve walking on a steep roof, or using a trad pole. Neither of which I'm very keen on. One of them is a monthly clean with no environmental effects like trees or roads making it dirty. So it's always very clean from one visit to the next. For this reason I am going to try the dragon fly on it. Even though the dragonfly isn't designed for outdoors I figure it should work since they are so clean. The other, is every three months. So it gets a lot dirtier. I could use the dragonfly but it would probably take some hard work, based on my experience with it so far, and would be quicker to do it by hand. So two questions really; Anyone got any better ideas? And anyone know what it is about woof effect uPVC that causes this phenomenon?