Filtering water at home is a sequence of decisions rather than a single purchase. Test first so you know what you are treating, decide whether the treatment belongs at the point where water enters the house or at the tap you drink from, put the stages in the right order, then set up the maintenance that keeps them working. Skipping the first step is why most households buy the wrong equipment.
Step one: find out what is in the water
Every treatment decision follows from a result. On a public supply, start with your utility's annual Consumer Confidence Report, which every community water system publishes and which the EPA maintains a finder for; it tells you the source, the disinfectant and what was detected. Add your own test for anything the report cannot cover, principally lead, which comes from your service line and fixtures rather than the source. On a well, there is no report at all, so a laboratory panel is the starting point. Test strips are useful for hardness and a rough chlorine check and not for anything that matters at trace levels.
Step two: choose point of entry or point of use
Point of entry means treating everything as it comes into the building, which is what you want for hardness, sediment, chlorine, iron and anything affecting bathing, laundry and appliances. Point of use means treating one tap, normally the kitchen cold, and it is the efficient answer for drinking-water contaminants such as lead and PFAS, because you are treating gallons rather than the whole household volume. Many homes end up with both: a sediment and carbon stage at the entry to protect the plumbing and improve every tap, plus a certified cartridge or reverse osmosis unit at the sink for what goes in the glass.
Step three: put the stages in the right order
Order is not a matter of taste. Coarse sediment comes first so grit does not damage or blind everything downstream. Oxidation for iron, manganese or sulfur comes next with its own filter, because oxidised iron will ruin softener resin if it reaches the bed. Softening follows. Carbon sits after that for taste and chlorine. Ultraviolet disinfection, where it is needed, goes last, immediately before the house, because it needs the clearest water it will ever see. Reverse osmosis at a single tap sits at the end of its own branch, fed by water that has already been through the house stages.
Step four: build in the maintenance from the start
Every stage is a consumable, and the failure modes are quiet. Sediment cartridges announce themselves through falling pressure, which is why gauges either side are worth fitting. Carbon exhausts silently and the only symptom is the taste coming back. Softener resin needs salt and eventually needs replacing. UV lamps lose output long before they go dark and are replaced annually. Fit isolation valves and a bypass around everything so a change is a ten minute job rather than a house shutdown, and diary the intervals. Our whole house water filter guide covers sizing each stage to peak demand.
Questions people ask about how do you filter water
Is a pitcher filter enough for a household?
It improves taste for drinking water and nothing else. It does not protect appliances, does not address hardness, and its capacity is small relative to household use.
Do I have to filter the whole house?
No. Treat the whole house for hardness, sediment and chlorine, and treat a single tap for drinking-water contaminants. Whole-house treatment for everything is rarely justified.
Can I install filtration myself?
Cartridge housings and under-sink units are within reach of a competent DIYer, but backwashing tanks, softeners and injection systems need a drain, a bypass and correct sizing.
How do I know the filtration is working?
Retest after installation and again before each media change. That confirms the equipment is doing what it was sized for rather than merely being present.