People sometimes try to do good things, but not having proper information (or googling the wrong web site) they end up with a final result that is incorrect. As you look at this photo, what's missing?
This is a whole-house filter.
The house is on public water, but they have one anyway.
This filter is desperately clogged!
It looks to have not been replaced since installation.
Either they don't know to replace it, or it's too difficult.
So, what's missing?
Here, compare their installation to the filter instllation in my house, on the right.
Obviously the difference isn't the color of the filter!
You can see the important difference a little to the right of the filter. See it?
Before and after my filter I have a valve!
To remove the filter, I only have to turn off each valve and that turns off the pressure, and allows me to remove the filter cover and change the filter!
No valve, no remove. It's pretty simple.
The installation of the blue filter above does not have a valve on either side.
Number one, there would be too much pressure in the line to remove the filter cover.
Number two, the water in the entire plumbing system would have to be drained, AFTER the water main is turned off.
My house utilizes the best practice - the other house does not.
My recommendation: older homes usually have many homeowner installations. Not every homeowner knows how to do things, and not every homeowner wants to pay a professional to have things done! Your solution to this would be calling a home inspector before you buy that "newly remodeled" property! You never know what you will find out!