I've often thought that most of the water I use is completely wasted. I try to be much more economical these days.
You see, you need a good flow of water to rinse, but only a very modest flow when soaking and scrubbing.
These days I soak the window in the time-honoured way: top, sides, bottom and then turn the water off to give a good scrub. Then, turn the water back on to rinse.
I'm using maybe 25% less than before and I'm sure that I could save even more if I used a trigger rather than a ball valve.
Just a thought.
Of course, for maintenance cleans, this isn't necessary as the glass is usually just a bit dusty. It's only first cleans or very dirty windows that need scrubbing.