When we owned our HTT, it had a how house filter system, similar to the one Macrosill linked to. When we went to winterize it the first winter. The normally clear filter was orange and there was a lot of sediment at the bottom of the filter. We've always used a filter ever since.
We currently camp seasonally. Our campground has well water, which is tested on a regular basis (the owners use the same well water in their house). We just use one of the Camco inline filters. If we weren't stationary, we'd stick with one like Macrosill linked to.
-Michael