A filter tank is the standard shape of serious household water treatment: a fibreglass reinforced vessel with a control valve on top, a riser tube down the middle and a bed of media inside. What it treats depends entirely on what the media is, which is why the same installation shape covers sediment, iron, carbon and pH correction.
What is inside one
A riser tube runs from the valve down to a distributor at the base, which collects treated water and spreads flow during backwash. Around it sits the media bed, and beneath that a gravel underbed where the design calls for one, supporting the media and helping distribute flow. Above the bed is freeboard, empty space that lets the bed expand when it is fluidized during backwash. A vessel packed full has no freeboard and sends media out to drain, which is one of the more common self install mistakes.
Sizing on flow, both directions
Two flow figures matter and they pull in opposite directions. Service flow is what the household draws, and too small a vessel means water passes too quickly through the bed for the media to do its work. Backwash flow is what the vessel needs to lift and clean the bed, and too large a vessel on a modest well pump means the bed never fluidizes and slowly packs. Sizing is therefore a matching exercise between the house, the supply and the vessel, not simply choosing the largest that fits.
The media decides the job
Multimedia or sand for sediment. Catalytic media or manganese greensand for iron and manganese. Granular or catalytic carbon for chlorine, chloramine and taste. Calcite for raising the pH of acidic water. Ion exchange resin for softening or, in an anion vessel, for nitrate and tannins. The valve, the tank and the plumbing are the same in each case, which means a house needing several treatments ends up with several identical looking vessels in a row, in a fixed order.
Servicing and access
Media is replaced rather than cleaned, at intervals measured in years, and doing it means taking the valve off, removing the old bed and loading the new one through the top with the riser protected. Plan the access before the vessel goes in: headroom above it to lift the valve and pour media, and a route to get a heavy tank in and out. Fit isolation valves and a bypass. Our whole house filter guide covers ordering several vessels when the water needs more than one stage.
Questions people ask about water filter tanks
What decides what a filter tank removes?
The media inside it. The vessel, valve and plumbing are generic, so the same shape serves sediment, iron, carbon or pH correction.
Can I fill the tank to the top with media?
No. Freeboard above the bed is what lets it expand during backwash. A full vessel pushes media out to drain.
How is a tank sized?
By matching service flow, so water spends enough time in the bed, against backwash flow, which the supply has to be able to deliver.
How often is the media replaced?
Typically years rather than months, signalled by a pressure drop that a backwash no longer clears or by declining treatment performance.