A storage tank has two filter positions and they do different work. Filtering on the way in keeps the tank clean. Filtering on the way out decides what the household actually receives, and the arrangement there has to account for a pump, for the sediment that has settled, and for the fact that stored water carries no disinfectant residual.
Draw from the right place
Take the outlet a little above the floor of the tank rather than from the lowest point, so settled sediment is not pulled into the line every time the pump starts. Fit a strainer or a foot valve on the intake. Where the tank stratifies, the best water is neither at the very top, which collects floating material, nor at the bottom. Getting this right removes a surprising amount of load from everything downstream and costs nothing but attention at installation.
Protect the pump first
Most tank systems use a pump to pressurise the house, and grit destroys impellers and seals. So a coarse filter or screen belongs ahead of the pump, not only behind it, where it can be serviced without dismantling the pressure side. Behind the pump, where flow is steady and pressure is available, the finer stages sit: a sediment cartridge, then carbon for taste and organics, then whatever the water needs, then disinfection last.
Disinfection belongs after the tank
This is the placement that matters most. Water stored in a tank has no residual protecting it, sits in the dark with whatever settled material has accumulated, and is warm enough for growth. Putting the disinfection stage after the tank means anything the tank itself contributed is dealt with before the taps. Putting it before the tank treats the water and then stores it unprotected, which is the arrangement that looks sensible on a drawing and fails in practice.
Sizing for the pump rather than the mains
Flow through the train is set by the pump, which may deliver more or less than a mains supply would, and every stage has to suit that. An ultraviolet chamber in particular has to be rated for what the pump can push rather than for what the household would choose to draw. Fit isolation valves and a bypass. The EPA notes private supplies are not federally regulated, so testing after commissioning is the owner's. Our whole house filter guide covers the train.
Questions people ask about tank water filter
Where should the tank outlet be drawn from?
A little above the floor of the tank, with a strainer, so settled sediment is not pulled into the line at every pump start.
Should the filter go before or after the pump?
A coarse filter or screen before it to protect the impeller and seals, with the finer stages behind where pressure is available.
Where does disinfection go?
After the tank, so anything the stored water picked up in the tank is dealt with before it reaches the taps.
What sets the flow the stages must handle?
The pump rather than a mains supply, so each stage, particularly an ultraviolet chamber, is rated for what the pump can push.