I've been using a sprinkler to keep my plantings watered, and the rock
around the plantings and the nearby concrete is turning rust colored.

Is there anything I can buy and put in-line to prevent this from
happening? Ie. some kind of filter or whatever to remove the iron/rust
before it puddles on the rock and concrete?

I see the variety of soaker hoses from Fiskars and Orbit, but I'm afraid
those might not provide enough water since I have so much rock-based mulch.

Any advice would be appreciated!

Thanks