There are many types of filters based on the filter media. Charcoal (Activated carbon), cotton, resin bead (includes cation/anion and water softener), and special types for special contaminents like high iron, sulfates, dissolved solids, arsenic, and microbes. There is also reverse osmosis which uses membranes and "ionic pressure" (osmosis) to remove virtually all ions. Selection is based on the stuff that is actually in the water. You wouldn't for example spend $400 on water softener systems when your hardness is unmeasurably low. A sediment filter is a great precaution for any system "on the Road" - especially if you do employ a high dollar treatment system downstream. I can recommend to most to use a disposable cartridge type canister that is both a sediment filter and activated carbon. It will protect the trailer from particles build-up and reduce odor and chlorine. It has some microbe catching benefit but should not be relied on to sanitize water of unknown quality (like shallow well product). I never liked the term "City Water". As I have posted before, I don't use campground water to cook or drink. I installed an isolated, stand alone drinking water system I fill with 5 gallons of store bought water for these uses. For me and my family campground water is for bathing and washing.
So treat water for known contaminents, for desired uses. Filters only reduce levels - never completly clean up. Use them in combination for synergetic benefits and efficiency. Research or get advice before large investments.
If you don't regularly (continuously) use a given system, the filter canister will become a biology project. Just to mention it. As for that matter, any portion of the system will sprout velvet eventually. But particularly in filter media because that is where we want it trapped and then we throw it away.