When I first started, I was taught to squeegee with plain water - no detergent allowed. If you practice it works perfectly, just a different sort of technique and skill.
And it gets the windows clean
You had to take more care, and needed to be able to 'fan' without allowing the squeegee to stop or it would jump and leave a mark.
Being lazy, I realised it was easier with some sort of soap when I started up on my own