I see your point but then I don't. A cartridge filter could care less if there's a water shortage or expensive water, if the time comes to clean it has to be done. On the same token a large sand filter will give you the same mileage the cartridge would before you'd need to backwash so the analogy you give doesn't pan out. Simply put its all in the eye of the beholder. I have all combinations of pools and filters and can't convince myself anyone of them is better then the next. It's more about how diligent the owners are with what they have.I’d say if the pool get lots of rain that fills up the pool constantly, a sand filter seems to be just fine since you can backwash our the extra water for a free cleaning. If water shortage or cost was an issue, I’d go for the cartridge filter. After seeing the mess that happens with my fathers DE filter when it has to get cleaned, I wouldn’t want to mess with all that.