Where it comes from
Many Florida irrigation systems run on well water that's high in iron. Every time the sprinklers hit the driveway, sidewalk, or wall, they leave a little iron behind. It builds up into orange stains.
Why pressure doesn't fix it
Rust is a stain inside the concrete, not dirt on top of it. More pressure just scars the surface. Rust needs a cleaner made to dissolve it, followed by a rinse.
Keeping it from coming back
Adjust heads that spray onto concrete and walls. Some homeowners add a rust filter or treatment to the irrigation system. Without a fix at the source, the stains will come back.