I always use a charcoal water filter at the spigot in addition to our in rig water filtration system. When we were in MN a couple of years ago, I noticed our water pressure dropping. It turned out the spigot charcoal filter was totally plugged with iron. However, it had done its job as my in house filter remained clean and the water was clear. I write the date on the filter when I install it and change them at least every 90 days. I change our in house filter every 6 months.
Any water going into the tank also is run though this filter.