You can buy a shower head filter
Hey OP I have a hard water filter for ~30 bucks from Amazon. It works really well and lasts about ~4 months in a shower for two people. I have really thick snd long hair and I had flaky buildup and my hair was knotted and matted all the time. it’s made a huge difference for my hair and skin. It’s worth a shot because it’s not expensive. Here’s the filter I have
I purchased it on Amazon, it says it helps with hard water.