That reminds me, it's been a few months since I've changed mine... I usually go until the water seems to drop in pressure. I get far more grit in mine though than you show, like the bottom quarter will be full. I'd change it more often but it's a pain--old setup, getting hard to turn. We do use a Brita for drinking water though.
Sometimes I think it'd be nice to move and get onto town water and sewer; but those aren't free either.
Sometimes I think it'd be nice to move and get onto town water and sewer; but those aren't free either.