A water tank filter is the filtration you put around a storage tank: a screen or sediment cartridge on the way in so the tank does not silt up, and a proper filter on the way out so what reaches the taps is clean. Which one matters most depends on whether your tank is fed by a well, a cistern, hauled water or rainwater.
Filter the inlet to keep the tank clean
Anything that enters a storage tank settles in it. On a hauled-water or rainwater tank an inlet screen and a coarse sediment cartridge stop leaves, grit and insects from ever getting in, which is far easier than cleaning a tank out later. On a well-fed cistern the inlet filter catches sand and iron floc from the aquifer. Inlet filtration is deliberately coarse: it is there to protect the vessel, not to polish drinking water.
Filter the outlet to protect the house
The outlet filter is the one that decides what your fixtures see. It normally sits after the pressure pump so it works at full line pressure, and it is usually a two-stage arrangement: a finer sediment cartridge to catch the fines that settle and get stirred up, then a carbon block for taste, odor and chlorine if the tank is dosed. Size the housings generously so the pressure drop across them does not starve showers and appliances.
Tank water often needs disinfection as well as filtering
Standing water in a warm tank is a hospitable place for bacteria, and no sediment cartridge does anything about that. Cistern and rainwater systems commonly pair filtration with ultraviolet disinfection, which needs the water to be clear before the lamp can work, so the sediment and carbon stages become the ultraviolet unit's pretreatment. Chlorine dosing into the tank with a contact period is the other common approach on larger or intermittently used systems.
Test before you buy the cartridges
The EPA notes that private wells are not regulated under the Safe Drinking Water Act, which means nobody is testing a private tank or well for you and no annual report is going to arrive. A USGS study of 2,100 private wells found about one in five carried at least one contaminant above a human-health benchmark. A test tells you whether you need sediment control alone or iron, sulfur or bacteria treatment as well, and our well water testing guide covers what to ask for.
Questions people ask about water tank filter
Should the filter go before or after the pressure tank?
Put the main house filter after the pressure tank so it runs at steady line pressure. A coarse inlet screen or cartridge ahead of the tank protects the vessel itself.
How often does a tank system's filter need changing?
More often than a city supply, because tanks hold sediment. Watch pressure at the taps and change the cartridge when flow drops noticeably rather than on a fixed date.
Does a tank filter make stored water safe to drink?
Not by itself. Filtration handles sediment, taste and odor, but bacteria in a storage tank need ultraviolet disinfection or chlorination plus a lab test to confirm the result.