Were there any caravans that were manufactured without the installation of a fresh water filter?
After looking in the Haynes Caravan Handbook by John Wickersham, it doesn't clearly state if all caravans have a water filter installed and I can't find one on my 1999 Coachman Amara. There is only a square recessed external access for the water pump (no filter above like my old 1992 Coachman) and I can't see an inline filter anywhere under the kitchen sink or cupboards.
Changing filters IMHO is a waste of time and money. We never drink from the water system in the caravan because even if you have a filter ther is loads of bacteria after the filter, i.e. the water left in the pipes when you have drained down as you can never get them totally clear.
Swift Group vans have not been fitted with filters for at least 15 years. We have never had one, regularly drink the water, and have never had any problems.
We have never had a filter and drink the water and have never had any problems. If you are thirsty enough you will drink from a stream. The one problem that people have mentioned about filters is that they may end up with slime in them that would not normally accumulate.
If you are using water from a tap then hopefully it will be filtered somewhere in the waterworks treatment system. Unless you refilter your water at home then why do it in the van?