First question is what is it in water that you *think* is a concern? Just sediment? Microorganisms? Bacteria? Viruses? VOCs? Heavy metals? Taste and odor? There are different filters for different things and there is no inexpensive single catchall filter. The thing about RV-ing is that if you travel around much, you won't know what the water quality is like. Even treated water from municipal systems can contain contaminants. Some could care less about the water they drink tho.
Filters can be NSF certified or not and without it, they can claim anything on it's performance. Some filters have ratings for total gallons for lifespan before they plug up and some filters will be rated for flow rate (GPM). Low cost filters will have no certification of any kind of ratings and are plenty of them around. One concern for filters for RVing is that they can be exposed to warm temps. if left in the sun or in a concealed spot inside and the temps get warm enough to promote bacterial growth so you may want to remove the filters when not in use and put them in a fridge. When looking at micron ratings, you want one that is rated "absolute".
Carbon filters are for improving the taste and odor from chlorine. With a small enough rating, also act as sediment filter. KDF or sometimes silver in a filter does
not prevent bacteria from getting through, it is there to prevent growth on the outer portion of a filter. Bacteria will thrive on some sediment filters if you pick the wrong one.
Sediment-only filters are the easiest to set up and the least expensive and are typically rated down to around 5 microns and greater. To filter out microorganisms and bacteria, you will need a filter rated 1 micron or better. There is what's called an ultrafilter (UF) that is rated down to 0.2 microns and will remove some viruses.
Doulton makes some excellent ceramic filters like the
Sterasyl Some tech. info from Doulton is
here. Doulton has some good info. for RV filtration
here. Crystal Quest makes a UF cartridge, info.
here. There is more Crystal Quest info. but can't find it at the moment.
There are lot of point of use (POU) filter under-counter assemblies on the market with various levels of filtration. Watts has the Premier UF-3 3-stage under-counter filter setup with a final UF filter in the 3rd photo. The last photo is a common exterior inline filter that many RV-ers use and this one is rated 100 microns which is very coarse, can plug up quickly from silt and will let microorganisms, bacteria and lots of other undesirable "stuff" get through. It's not NSF certified and has no other specs. Some inline filters are better but you need to look at the specs. No specs, no buy.
The first photo is what was on our city water inlet screen after an early season camping trip (supplied from a municipal system). It's a biomass and is there because the CG failed to flush their water system at the start of the season. Yummy looking stuff. Looking into water quality after that resulted in me building a setup using 10" filter housings with 2 stage sediment filtration (63 & 5 microns), a 1 micron Doulton Sterasyl cartridge and a Crystal Quest UF 0.2 micron cartridge. The last filter supplies a separate drinking water spout on the counter. This produces water that is as good or better than bulk water at vending machines in a store.
