I just washed my car yesterday as the temperature broke 40F. I use two buckets with grit guards. The rinse water was pretty black even though I had hosed off the car well. What was under the grit Guard is enough to convince me that they are essential.
I just don't get how the water was black. Don't you rinse your sponge with hose water?
My sponges don't go into any bucket without looking pristine clean.
The bucket water lifts any microscopic stuff that I miss. I wouldn't want any other dirt or grime to be in the bucket! That's how cars get marred due to washing! Extreme care must be taken, and its not that hard! You just can't trust a band aid like a grit guard...