Greetings from Hawaii;

I've learned a lot just lurking on this forum as I've set up my catchment system.
I've seen Speedbump refer to a homemade filter using a softener tank and sand. I don't know if such softeners are available around here because there aren't many wells, mostly catchment. I was wondering if I could make such a filter out of an old water heater tank. The only problem I see is putting some sort of screen on the bottom of the cold water tube. Any thoughts? Thank you very much.