The problem with filters is that under "normal" caavan use they spend a lot of time sittng around with nothing passing through them, for instance a week or more at a time.
However, during that time, bacteria and algae have time to multiply,not good.
As for the in line Aquasource filter you should find that in probably the most inacessable place under the sink, it is about 6 to 8 inches long, cylindrical in shape, which should be fully removed for winter storage, as after last winter it was found on many vans to have split, not just in a small place, but from top to bottom, behind the label, so not easy to see until lots of water come gushing out when the pump is run.
Personally I believe filters to be a total waste of money and a source of possible infection.
All that is really needeed is a gauze filter to stop any large particles entering the system and blocking the taps.
Only yesterday I was called out to a van which had very poor water pressure , only to find the pipework and taps blocked almost fully with carbon granules from a failed filter.
If you have an Aquasource filter I would strongly recommend removing it completely and filling the gap with a length of the same pipe as fitted.
The water quality in the UK is very good, there is no need for extra filtering.