If you have streaks from soap, they you are waiting to long to rinse. Wash in sections ad rinse thoroughly. The old rubber roofs were usually the reason for white streaks.
If it is white water stains from hard water, then an acid rinse. Mix vinegar with water and do a test area to see if that will remove it. Blue Beacon does a mild acid rinse but it will take all the wax from the side. I don't use them anymore for obvious reasons.
A complete and thorough wax job is expensive but that will likely solve your white streak problems
