Full-timers' perspective here. Our previous fifth wheel did not have a built-in water filter. We used the blue Camco filters and left them in place for three months of full-time use (had a reminder in the calendar that popped up). Our new Solitude has a built-in cartridge style filter (like in a house) and we'll follow the manufacturer's recommendations on that. For drinking and making coffee, we have a separate water filter pitcher we keep in the frig. Municipal water supplies (and the well system at the park where we are now) are safe - they just don't always taste good. With the double filtering (including at least one carbon filter element) what we drink tastes as good as anything we can buy at the store - and this method greatly reduces plastic waste.
Rob