I am working in a very old house, and this tank is sitting in the basement, connected to an expansion tank. The water for the house comes from a well. The water from the well comes into the expansion tank, then to this tank-looking filter, then to the rest of the house.

I assume it's a filter system.

Question: what criteria would I use to determine if it's worth replacing this filter system?

What is the current standard for whole-house water filtering system? In other words, what should I look for when searching for a replacement? (Not asking for brand recommendations, but for types of filters to search for)

Any suggestions appreciated. dial


  • 1
    @Ecnerwal Thanks. Added a picture.
    – Cheery
    Sep 11, 2023 at 1:56

2 Answers 2


Given nothing else around this tank I'm thinking it might be marble chips (or there used to be marble chips, depending on how long it's been neglected) to neutralize acid water and keep it from eating pipes and old leaded solder joints.

As for what, if anything, to replace it with - get a laboratory test done on the un-treated water straight from the well (you might have a minimal one from the time of purchase, but the most minimal one really only tells you if it's got bad bacteria or not.) When you know what it has got in it, you'll know what to treat for.

There is no "standard" filter system because wells produce water that may need no treatment at all, a little bit of treatment, or a whole lot of treatment, depending what the water they are drawing from has in it. And there are choices of different ways to treat various issues that water in need of treatment may have.

I've lived with wells all the way from "tests very nearly like distilled water" to heavy black sulfur, significant iron, and extremely hard. They need different things done to them to make the water acceptable, though I ended up just hauling drinking and cooking water at the black sulfur well house.

While you can try to DIY testing with test strips, my experience is that an actual lab test (or a colorimetric test at a well-equipped plumbing department, for the things they test for) is far more reliable. You could reasonably expect to get a ballpark on pH that way. But that's only one of many potential things to deal with.


It's a granular medium filter as evidenced by the filter vessel not opening at its full diameter (as it must for a cartridge filter). what medium is in there it's hard to say, for example it could be sand or diatomaceous earth,

Also back wash is a thing with granular filters as the upwards flow loosens the medium releasing the trapped residue.

to backwash, select backwash an open the spigot (you probably want to attach a hose first) let water flow water until it looks clean.

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