Here’s a little confusion many people face. A whole house filter is not the same as a water softener. The filter catches physical junk like sand and rust. The softener removes minerals like calcium. If you need both (and many homes do), install the filter first.
Why? Because the softener works better if the water is already clean. It’s like washing your face before putting on moisturizer. If you put the filter after the softener, you risk clogging the filter with the softener’s own resin beads. That’s just silly.
